thonet rocker  

No pic
There's no picture, Whitespike.

Oh nuts!
Oh nuts!
http://austin.craigslist.org/fuo/839199647.html

there are so many knockoffs o...
there are so many knockoffs of this chair out there (they were retailed all over in the 70's and 80's) that it is unlikely. But when I am not sure, I go look in person. In general I steer clear of ones that have been excessively knocked off (cesca chairs come to mind). I recently looked at and bought some sorta barcelonaesque chair that had bad pics from the top only so I could not see the frame. It was a fabulous Kurt Thut piece. So now I know, when in doubt, check it out.

He's right
Whitespike, there is at least one if not more in every antique store in the country. That one that you posted does at least look like it could be from the 30's or 40's but I wouldn't go there if it doesn't have a label of any kind to confirm Thonet.

But it's $25. And what's the...
But it's $25. And what's the likelihood of a label on a 30s-40s chair?

I would snap it up.
But have a ride in it first.
If it has a nice 'lean back' and balances nicely on the back tilt...
It is a perfect newborn rocker.
Unlike an Eames shell rocker base, more upright, the thonet has a nice
resting feel. A recline.
The price is good! The listing mentions a varnish issue. That could hint at the
age but it could have been used outside.
I bet the owners could give you a history.
I would not hesitate.
That is a small price for a rocker that may be perfect for you.

damn
As it turns out my wife had a grody old aunt that used to sit in one of these. She doesn't want it bc of that! Haha!

Rocking Chair issues
A pregnant woman's opinion on a rocking chair should be listened to at all times. Give her some more options. This could be a great thread. What should Baby Whitespike be rocked in? I like this Hans Wegner rocker.

I love the Wegner! With a...
I love the Wegner! With a new job, and a youngin' on the way my days of spending serious cash on a chair are over for now!
The Thonet price sure is tempting, but as you correctly pointed out, the lady is to be considered first.
I like this one okay below. The fabric would have to go!!
http://austin.craigslist.org/fuo/848464557.html

I would prefer a danish rocke...
I would prefer a danish rocker of sorts.

.
Not old, not Thonet...

Hans Olsen
I'm working on one of these as we speak to ready it for sale. It is a Hans Olsen for Jorgensen Mobelfabrik or Juul Kristensen (conflicting attributions)from 1963. Interested?

This is a rocker designed by...
This is a rocker designed by Gustav Siegel for J&J Kohn in the early 1900s - I've had it for some years and even though it gets shunted from spare room to spare room I've never had the heart to sell it!

GlassArtist
I love it!! Unfortunately, I have to look for a steal this time, and I don't steal from friends! Curious, though, how much you're asking for it...