I went with a 560 sli set up and get scores at about a single gtx 580.
The price on the 560ti will come down and has during sales. I'd wait till the 560ti hits the 170 ish price and get a 560ti.
If you had to jump in now, I'd have you look into a gtx 480 that is closer to a gtx 570 and at the cost of a 560ti.
SLI works for me. Others hate the idea and some fear (overblown imo) micro shutter. It tends to be a better idea to get the best single card you can rather than SLI.
psu/mobo ? what is your budget and do you want to OC a SB or go stock IB?
This is somehow strange, 2 x GTX560 should be far better than a single GTX560Ti, but its not what I see in many tests.
OC is not in my plans. I like to walk the safe road.
On the GT480 stuff, it is a very nice idea indeed, but I heard this card is quite noisy, big and power hungry. Is that true? If not would be a good option for the same price range.