The GT owns the 640/320GTS, not the 512MB GTS. For $170, very nice indeed. Only lasts until the end of 8/5, so you only have today to buy it.
I'm not sure only fools or fanboys should get this. The 8800GTX is only slightly better then the 9800GTX, which is only slightly beat by the 4850. I'll bet the 8800GTX is only slightly better then the 4850, in some situations. Seeing as you aren't spending any more then the 4850 (with no rebate on this one) the deal is only pretty good.