The 650d sensor is newer, with a newer processor, so theoretically it should give better response. except for certain websites that shall remained unnamed by me, saying that the 650D actually turns in slighty worse IQ than the 7/60/600D. Of course, if you're looking *that* closely at images from any of these, you should look for a good deal on a used 5d2 instead.

The biggest selling points for the 7D when I bought it were the fps and the AF, it's much more 'sports' oriented. 'sports' doesn't have to mean people running around a field, or birds flying overhead, kids running around a house can be just as challenging for an AF system.
Of course now that I've got it, there's other benefits that I wouldn't have thought of. I tried a friend's 550D the other day. Man, it is tiny. I've used rangefinders which are also small, but they fit my hands better. If it's an slr it's gotta be big for me.
And i don't like the 550d viewfinder, too small and dark. Pentraprism ->>> pentamirror. once you get used to it you can't go back.
Electronic level, very useful for tripod-landscapes, especially pano-stitching.
And custom-functions. I know lots of people who have C3 set to "OMG, look, a bird!" mode.
I love the wheel/joystick combo, I can't live without it. But that's more of a baby-duck syndrome, if you're used to buttons you may find it hard to switch to wheel. ditto touchscreen, if you like it and use it, you may miss it...