im on 2 xfx hd5770 in crossfire and its a wonderful "decent" card. it'll do 1080 on max on most games out today (so ive read). this card is best bang-for-buck for quite some time.
If you can afford to buy 2 of these for Xfire IMO you should consider getting a single GTX470/HD6950/GTX560ti.
Before buying this card do some research on how well this card over clocks. I have 2 Sapphire reference HD5770s that run stable a little over 1GHZ on the core with air cooling.
This card runs cool and a single card can game decently. Single card would be ideal for a HTPC build IMO.
These cards scale well for Xfire. If I had a MB that could do 3xPCIx16 I would be tempted to buy another HD5770 for triple Xfire.
Using one in my computer(which uses an htpc case). It's not silent but it's very quiet. I only notice the sound because the computer was silent before the upgrade. Overall I'm extremely pleased(and I paid $200 QQ). Mine overclocks very well too.
Wish I hadn't read this. My bank account's already hurting, but I've always wanted to crossfire it.