An interesting point about USM motors, I hadn't seen this before. It goes against my expectations as USM motors are known not only for their speed, but also for their precision. Does this also apply to micro-USM? (N.B. the Powershot SX1 IS had a USM motor.)
I don't have a source for the USM-comment, so it might not be correct, but it could be one reason why Canon seem to lag in CD AF speed.
You need a high framerate from the sensor to get fast CD AF as CD AF analyze the video signal to focus the lens. PD AF use sensors that can determine how much out of focus the subject is and send an instruction to the lens how much closer or further away to focus.
CD AF can't to that, in stead the algorithm take one reading from the video stream, move focus a bit and check again. If focus is better (higher contrast) on the second reading then fine, it moved focus in the right direction and continue to do so until contrast decreases, then focus in the opposite direction. It will continue with this with steadily smaller focus shitfts until it can't get it better.
So, obviously doubling the frame rate mean it can do twice as many comparisions per seconds and get half the focus times - in theory. In practice focus speed will depend on two other factors (at least). The first possible bottleneck is the image processor which have to be able to keep up with the frame rate the sensor can deliver. That shouldn't be much of an issue. The second and possibly much more difficult obstacle is the lens which is designed for PD AF and not for small extremely fast repeated focus shifts. Which mean that the system is limited by how many times per second focus shifts can be done, and maybe how small shifts that are possible - I don't know enough detail about this to say where the real bottlenecks in the lens are. Maybe the focus motor, maybe mechanical tolerances contribute, and maybe the electronic protocol between body and lens is a limit.
Anyway, Oly/Panasonc added two new contacts when they moved from FT to mFT to improve AF performance and maybe Canon need to do the same, maybe not. I just hope they solve the problems so I can use my current lenses when they come out with a mirrorless system.
My comments about at 1000D successor being a new small camera didn't imply a higher crop factor at all. I can't see any reason why Canon shouldn't be able to make a 1.6 crop dSLR significantly smaller than 1000D.
All the last Canon superzooms SX1 IS/SX10 IS/SX20 IS/SX 30 IS (and I believe, alse eralier models) use an Ultrasonic motor, but not for focus. It's used to provide silent motorized zoom.
