Must ask all above if you regularly shoot at f/11 or higher, i.e. 16, 22 and so on?
Do this and do report back after you have shot a white or constant blue sky
To answer the original question - I personally think the cleaning system is a gimmick.
Had a 400d for a few days when they had just launched and would only swop my 350 if the 400 came with a 300 f/2,8.
Most dust specs on the 400 didn't move despite repeated on's and off's.:shrug:
Ask yourself - if the dust moved, where would it go and how long would it be before it found it's way back to the sensor