how much success with research?  

I have had good success. For example: http://www.designaddict.com/forum/Identification/sofa-Wegner-for-Getama

leif - That response is fantastic. I would frame that!

I prefer the personal touch of a telephone. I find it is easier to locate and speak with the "decision makers" while at the same time it is more difficult for them to say no.
I have received all the information I desire and made many long lasting contacts at Herman Miller, Knoll Chicago and corporate headquarters, Fritz Hansen and many others discussed on this forum. The cost of a recent telephone call from the southeast United States to New Zealand is meaningless compared to the "no charge" service I received (along with a corporate invite to the recent NYC ICFF show).
So called "fan mail" or "positive affirmations" to the designer are suitable for email. Based on my mother's philosophy of "you catch more flies with honey" I have always received a reply from the designer (Richard Hutten, Richard Schultz, Philippe Starck et al). On occasion they will call, as was the case with Richard Schultz. I was both pleased and surprised (we discussed the case study tetrahedron sculpture on his property).
These are my stories and my experiences and I am sticking to them. It works for me.

niceguy - you probably have something there. after striking out with the NY and NC label law depts. i talked to a man at American Law Label Co. These are the people who print the labels with manufacturer name and reg # and send it to them. Although it ended with no results he took the time to contact the various companies that he dealt with and ask if my reg# was theirs. Before becoming self employed I had a boss breathing down my neck all the time. Sometimes I feel like a phone call is asking for too much of someones time.

I've had mixed results. I think it depends a lot on the company that you contac and the person who answers the phone or the email.
I had a set of early Wegner chairs a few years ago with a shellac finish that the owners were sure was original. I wasn't sure at all, plus it was totally trashed and the chairs looked awful. If it wasn't original, I wanted to remove it and oil the chairs. They were made by Johannes Hansen, which of course no longer exists. I remember calling or emailing someone about them and not hearing anything back, then in desperation I called PP Møbler in Denmark and talked to a very nice gentleman there who advised me to call a place in NYC who handles their restoration work in the US. So I did, and talked to another nice gentleman who said no, the finish was not original---so it did take a bit but I was ecstatic to get that answer and now the chairs are pretty again!
Another time I had a question about my Jacobsen swan chair and got a very helpful person at Fritz Hansen via email. Have not had good luck at all with Knoll or Eames Office.
Those are hardly enough examples for a scientific sampling, though. Again, I think it just depends. But it's always worth a try!

spanky - I found a very helpful gal at Knoll when trying to date Bertoia chairs. She even sent me an email to make sure I received her first response. I'm sure I still have her name around here if you need it.

powbum,
Success with a telephone call. This morning I spoke with my contact at Knoll regarding replacement feet for one of my Pepe Cortés Jamaica beech-wood seat bar-stools for Amat-3 (not the new BD Barcelona derivative). They are sending the five feet (with a few extras for the future) at no charge. At the same time I was able to re-connect with my former contact at Richard Schultz Design (she had previously sent a full bag of replacement feet for my Topiary furniture). Another good day.. I always want for nothing from Knoll.

Well that sure worked out.I think what I run into more often than not, at least with American furniture, is the big fish ate up the little fish and the records were not important. It's a shame but I think a lot of this history really is gone.