My 9800gx2 can't even handle age of conan.
so yes. things are only going to get worse.
if you're the type who doesnt care about using top settings and the highest resolution your monitor can handle, then no you wont need to. I've spent a small fortune on this pc and monitor so i'd like to be able to get the most out of whatever I play. things get demanding at 1920x1200. heaven forbid I save up and buy a 30" for 2560x1600 XD
Depends what you want to do. For most people. No. For people like me, yes.