Trex decking  

I would suggest
researching on google and linking to home and restoration sites.
Many of them out there.
Personally i don't like the material for many reasons but this
is not the place to discuss decking material, imho.

IMHO
But cement block is OK? Just where do you draw the line, rockland? uh, imho.

I see nothing wrong with discussing decking material here
Which doesn't mean I can offer useful advice, however.
I will go on the record for being anti faux wood grain, though. The fact that it's a man-made material doesn't offend me, I'm sure the stuff has its pluses. But, why does it have to ape wood?

If we can...
...discuss field stone patterns on LRF's home why not Riki's recycled decking?
Yes, we can!...In my humble opinion these recycled materials smell green washing. I know to well that the way we recycle leaves us with quite a quantity of un-identified plastics. Not al plastic products are sufficiently identified with the appropriate symbol and not all plastic applications use only one kind of plastic like PET bottles, so what do we do with the un-identified ones? Mixing them with wood dust is one way and we have come a long way in being able to extrude them as the Trex catalogue shows. But it is not the right solution for un-identified plastic recycling. On the other hand, it certainly is good decking material, it also safes a few trees and space in the dump where these plastics would end up otherwise. It will not require any maintenance, no toxic painting etc and in spite of that negligence it will last a few centuries...unless your home burns down. Nobody has this kind of wish but it happens. What happens to un-identified plastics embedded in wood particles?...If it contains PVC it will create a very effective poisonous gas. PVC siding is flame retardant to a large extend and firemen know what to do when they see PVC windows and siding...but what do you do with this cocktail? I would not do it Riki, not that I know all the reasons in favour nor all those against but when in doubt?at least imho

Have you seen it in person?
Some of those products look awfully plasticky and fake. The ones I've seen look passable in one or two colors but not the other colors.
I've also heard that they get very hot in the sun and that they get oily stains, which could be a problem if you grill or eat on the deck.
As for environmental concerns, wood decks have to be stained and/or treated with preservatives regularly to keep them from rotting and falling apart. Six of one, half a dozen of the other? Pressure-treated wood is kinda sucky stuff, too, I think.
My dream is to have a very simple ground-level deck of wood or Trex-type decking in our back yard. Someday I will have it and then I'll have a place to put my eight Hardoy butterfly chairs that are currently stacked on the grass, kind of serving as abstract sculpture. I'd much rather sit in them!

Avoid Plastics
I know the planks you're talking about. I've inspected them as an alternative to my current wood deck. The low maintenance & longevity make quite them attractive. Cosmetically, They're too plain for my taste.
As Koen & Spanky pointed out, then environmental impact of plastics can be quite significant. Using wood can have it's negatives as well. My general rule of thumb...general rule...is to avoid plastics for any major installation unless absolutely necessary.

" They're too plain for my taste."
If that's the worst that can be said for the aesthetics of a "background" material -- I say, right on !
What is the curious-shaped "beam/plank" shown above ?
I've been hoping to find a good-enough and cheap-enough plastic "lumber" to use for outdoor (and indoor ?) furniture. Any other stuff out there ?

I'm guessing that the T-beam...
I'm guessing that the T-beam was designed to get around this material's flexibility. Is that the right word? It sags. It's ok for decking as long as the joists are of something rigid and it doesn't have to span much distance. But they don't make conventional joists out of it because they will sag. I'm thinking this T-beam is their solution to that problem.
Another thing I don't like about it is that it feels plasticky to my bare feet. It's not a beautiful material.

TEAK?
How about teak wood decking?
I am a carpenter and I have installed to many composite decks, they just dont look good to me. I like to call them Little Tykes decks.
http://www.ecosmartinc.com/catdeck.php

not an i-beam
it's a bit difficult to determine the scale of the extrusion, but it looks to me like a handrail which can accommodate standard-dimension [1.5"] spindles on the bottom open end.
aside from that, i've seen many installations of this and similar product over the years, and for the most part i remain unimpressed. however, just a week ago i saw some used in a concrete stairwell, and the results were quite attractive. it took me a while before i realized the medium-grey material was not concrete stamped with a woodgrain relief.
in my limited exposure, the "boards" were way too rough for my liking, which makes me wonder if the wood component of the product is somewhat unstable and therefore responds undesirably to weather conditions [moisture, heat, etc.]. or perhaps it's a necessary characteristic to enhance traction on a wet surface. either way, i remain largely unconvinced.
as to sourcing and comparative shopping, i think there are a number of manufacturers producing the stuff; it's more than plausible they each have their own recipe for the goop, resulting in a variety of properties and characteristics. if i were investing in this stuff for a project, i'd do a heap of homework before laying down the coin.

Teak
That teak deck is really beautiful! I really don't like how fake the Trex stuff looks either but pressure treated lumber warps down here in South Carolina in the heat and humidity no matter how diligent you are with the sealants.
SDR- that picture of the t-beam thing is the top hand rail that goes around the decking and the balusters (bannisters?) are inserted up inside it. That one that I pictured was the only "plain" one on their website. The other options all have ogee edges or other various molding effects that just looked Colonial or Arts & Crafts-ish to me.
I hadn't really thought about this Trex stuff sagging. I thought one of its main selling points was that it was supposed to be so durable.

Trex is not so green
I agree with Koen. trex is a green-washed product. I claims to be green but really it just moves the problem of plastics waste to a new place. Yeah, it saves a few trees, but not much more than that. AndI agree it's ugly a sin. You have to pre-drill and countersink every single screwhole if you want to avoid nasty bumps around every screwhead. And the person who mentioned the oily stains is correct. The plasitc sem to have an afinity for oil that even googone can't break.
If you want to do something truly green, get either reclaimed lumber or FSC-certified lumber. Please don't get teak unless you get it sustainably harvested. It's being over logged. Ipe wood is another good option.

uh oh
I was snappy.
But great to see a good series of postings. Trex has been on my disaster list
for a long time. Most of the searches are still there when googling.
Even a law suit i think.
Earlier Trex and similar products are being replaced left and right. Off to the
landfill. Another green not so green...
Now a mold issue has come up and may be coming from inside the product.
Concrete block has a grand history. Lottaliving has an ongoing thread of
patterns from the 50's to some new ones being made now.
I've been apologizing all morning. I sprayed the bath with cleaner first thing
this morning but didn't scrub, got out the vacuum hose for a quick gunk in the
slider track cleaning (dog food and bugs) but left it across the floor.
I created a slip and a trip.
Now the dogs are fussing. I think i'll go toss a ball...

my mom
My mom has a deck made out of some recycled plastic/wood composit thing. I dunno if it is trex exactly.
Without entering the green debate I like the material simply as-is, with no pretense of the embossed wood grain. Embracing new materials is something that all designers should do, without the need to gloss it over as something else.
However, my knowledge of plastics is somewhat limited - this stuff may very well be as toxic as people have claimed.