I have to ask, what ASUS 3870x2 did you buy? I think they have 3 out there. I own one of them, the ASUS EAH 3870x2 (4 DVI Slots, recycles air). I love this card and have owned all ASUS cards (A total of 6, last one was a ASUS x1950xtx). My laptop, motherboard, powersupply is all ASUS. Never had a problem haha.
I wanted to point out one thing tho, you said that your card only finds 512mbs of memory. This is true and how it should be. It should be showing 512mb per core. Making a total of 1 gig. In reality, its just a marketing trick when you look on the box and see 1 gig of ram!
Now i am waiting for the price of the ASUS 4870x2 to drop! Sorry to hear you had a problem with the fan! That really sucks because RMAs take forever (not with Amazon tho, they send you a new one and wait for you to send the old one back!)