Mr. Mister said:
Well, I'm guessing the next Mac Pro update, accompanied by GPU updates that will probably include DX10 cards, will be in January. So from a "grand scheme of things" perspective, it's terribly dumb since you're buying the last of a generation soon to be superceded. However, if you want decent graphics performance whatsoever until then, it's your only choice. I'd personally say go for it, you can easily sell it off for maybe even more than you bought it for to a 7300GT user who doesn't want to pay $500 for their X1900 XT upgrade kit.