Yes, the X1900 was put in the bag and box the 4870 came in and now sits in my closet. I'll keep it around in case I ever sell my Mac Pro for a newer Mac Pro so I can keep my 4870 :P
But, yes, even a few days later, my card works great. Absolutely nothing goes wrong. And I also can't hear a difference in idle fan sounds and think the 4870 is quieter while gaming. The X1900 would rev up its fans when I played World of Warcraft, my 4870 sounds like it's still idle after playing for hours at max settings. I don't know if it's because it can handle more and hence WoW isn't taxing, but I've yet to hear the fans rev up. Same with using it on Windows 7, the card stays relatively silent.
I think it's a smart purchase if you have the extra money.