Real world SLI experience

Im putting together a new rig ( time to lay the old XP2500 to rest ). I got a good deal on a PNY 8800GTS and it's going into an ASUS M2N-SLI dx board. Before I put everything in the case this weekend, I was wondering how practical for overall performance adding a 2nd 8800 would be. Reviews and benchmakrs are one thing, but I'd really appreciate some real world input.

Thanks

Farhang, thanks for the reply. I already have one GTS. Is the practical performance increase worth the expense of a 2nd card (and a new case big enough to accomodate an SLI setup). This is what I have so far:
M2N-SLI dx
Athlon 64 X2 4800
WD Raptor 74gb x 2
2GB - Crucial DDR2 6400
and the GTS 8800 320mb

I've heard of one or two people talk about have two of those cards in there system, and games like oblivion they can play mostly maxed at the highest res and they say it's smooth, and they complain about anything lower now, so...