I like this idea and we have talked about it before. The problem with this idea is that some people will be able to abuse it in order to avoid points expiration. Points do not have an expiration date attached to them rather it is a calculation done on an account. If points can be transferred to a second account and then transferred back, the expiration would be bypassed.
Wow, I never think about how criminal energy could infiltrate everything…
The idea of a “Thank You” button is nice in its own right, though, even without financial/point advantages attached to it. A kind of “Brownie points” or gold star treatment…
Vera and Mark, you would certainly be swamped with little gold stars!
Over at wikiHow, people have talk pages. When you want to thank someone, you can post an award or a thank you note to their talkpage. Some of the awards are very pretty. The ability to talk by talkpage and to exchange awards etc leads to a greater sense of community. Just as an example, you can see a page with quite a few picture notes and awards etc here.