I've got the intouds3 6x8 and love it - also have the 4x6 for my laptop. I was very surprised that I could adjust so quickly every time I use it, so it's surprisingly not a problem.

A friend of mine has the big one (9x12?) and won't go any smaller. While that just seems entirely too big for me (and would take up all my desk's real estate, BTW - it's HUGE!), he loves it.

Yeah, I've gotten to the point where I now even do about half my online and regular selecting and clicking with the tablet - I've dropped the mouse for a lot of things (I was at a PS seminar and the guy used his tablet for EVERYTHING - I thought he was nuts, but here I am now... oh well...).

I would probably advise the 6x8 flavor of whatever you get (Wacom, Aiptek, etc.).
Hope that helps - good luck!
-Lew ;-)