I can think of a few reasons why I would get a 560ti but my 470 died and I was RMA'd a 560Ti quite happy with it really. If you can get it for free then go for it otherwise deal with it
1: Most 560TI brands are preoverclocked cards come close to 480/570 performance
2: The 560TI doesn't hit temps anywhere near as high as the 470, it consumes less power produces less heat and less noise. My 470 annoyed the hell out of me on games it just destroys FPS wise, forcing me to force vsync as the high framerate starts the oven. I can imagine it being a fan assited oven with SLI.
3: That extra RAM the 470 has is only going to put to use on resolutions above 1080p below that the 560ti wins. Or the odd game that actually uses very high res textures. There ain't many, and the 560ti can cope with high texture pack addons from what I have seen of it so far.
Better option just wait till the 28nm cards are out.