From a video point of view I would be interested in if the new 650D is any cleaner in the shadows and at higher ISO's. The Q-scale function also interests me (user set video bitrate)
I don't run ML. Camera does all I need without it, so for me that wouldn't be a deal breaker.
Paul - You make very good points. The Q-scale is interesting. Since you mentioned that you don't use ML, you might or might not already know this: ML allows you to set a higher (or lower) bitrate on the 600D/T3i (which sounds like the Q-scale).
By chance, I was experimenting with this recently and it works - though not without some qualifications. The ML bitrate multiplier has been reliable for me at 1.4x (with audio on). Of course, this comes with a resulting larger file per minute of video. With audio disabled, I was able to go up to 2.3x reliably. I can achieve 3.0x in a low dynamic range environment (even with audio). Of course, the benefits of a higher bit rate are also less apparent in the latter case.
The highest (video-only) resulting average bit rate that I was able to achieve without the camera stopping the recording was a little north of 100 Mbps. Again, I shot at 3.0x indoors, but the resulting bitrate in that situation was only around 70 Mbps. Quite nice resulting picture, though not night and day compared to 1.0x. And, a test at 0.2x at 7 kbps was completely watchable, though I wouldn't ever use it for a serious video. Of course, the bit rate can't solve the 600D's moire/aliasing problems nor can it increase the actual resolution. But, it does what it does.
I mention this in case you tried ML a long time ago and might consider it again, given your interest in Q-scale. The latest version (from December) has been very stable on my 600D.