In a game optimized for SLi performance, the two GT's will rip apart a single GTX or Ultra, and will shine especially if you game at a resolution over 1280x1024.
There really is no reason to buy a single GTX over even a single GT for twice the price. From what the reviews have said, the GT is just about on par with a GTX. Maybe just a smidge lower.
Haha yes, if they haven't already.
This card seems extremely popular. If you're looking to buy, then this is a good time to jump on board with SLi.
Make sure you have the CPU and power supply to handle it though.
Case: Antec 900 ATX
CPU: Q6600 (i will probably oc it sometime to around 3GHz)
Cooling: Zalman CNPS9500 (with LED)
PSU: PC Power and Cooling Quad Silencer 750W
Mobo: ASUS PK5N32-E SLI
Vid. Card: 2x PNY XLR8 8800GT (in SLI)
Memory: 3GB Crucial Ballisitx DDR2 800MHz (2x1GB,2x512MB)
Hard Drive 1: Raptor 10000RPM 150GB
Hard Drive 2: Seagate 250GB 7200RPM
DVD: Two 20x DVDRW w/Lightscribe
OS: Vista Home Premium 32-bit