i havea 9x12 by virtue of ebay. it's just an old intuos, the offwhite color, before they came out with intuos 2 and 3 and 15 or whatever they're on now. i paid about 1/3 or 1/4 its original retail price, and it still works beautifully.
it is very big though. i think the 6x8 may be the perfect compromise, really, unless you have a HUGE monitor and need to do something super-large-scale.