I think the 6x8 is a nice size. I got a good deal on the 9x12 version of the older Intuos, so I went with that. I certainly wouldn't want anything bigger!
The biggest advantage of the 9x12 (and larger) sizes is that you have the option of "splitting" the tablet area into two regions - Wacom calls it "QuickPoint". On the 9x12, you get one that is small (about 3"x2.25") and one that is larger (9" x 6.5" or so). Both regions map to the exact same screen area. So you "point around" in the smaller one for moving quickly without a lot of hand movement, and "point around" in the larger area when you actually want lots of detailed "motion capture", for when you are retouching for example.
Of course you can quickly switch to using the whole 9"x12" tablet for the whole screen (and back again to "QuickPoint" mode) at the touch of one of the "menu strip" buttons at the top.
Big fan of the Intuos 2. I'd recommend it for the pen design alone. Bigger, more ergo pen, with a non-slip grip makes for much easier working environment.
So for the same price as the 9X12 you wouldn't go for the 12X12???
No, because to me, anything larger than than 9x12 wouldn't be necessary. If at all, a nuisance; because the square tablet compared to the rectangular monitor will distort your drawings.
