Some professional photo/video and CAD/CAM apps could potentially use that much. But if you use them, you most likely would know that already. Besides that? Makes a nice space heater, I guess. Good for the e-peen...
One of those questions where if you have to ask, then the answer is probably "no".
<...and please don't mistake me for a 2GB/XP holdout - My own system has 8GB and I've been running 64 bit OS's exclusively for the last 3 years.>
Yeah that about sums it up^ if youre buying an alienware youre using it for gaming and in all truth you wont see any real fps/performance gains from such a ridicolous amount of ram.
On an opinion note i would avoid alienware just from a cost standpoint. Youre going to pay 4-6k for something the following year you could buy for 1500-2500 bucks. Youd be better off buying a reasonably priced one and upgrading it every year.