A few notes on camera features and settings.
Autofocus:
I've made several hundred test shots using the AI servo mode of the 50D on several different lenses. I've tested primes and zooms. My mainstay lenses are the 24-105L IS and the 70-200L IS, and with these two lenses I'm seeing between a 70-85% in focus rate using my dog Hans as a moving target. The 70-200L seems to be a better performer than the 24-105. This isn't bad. About the same keeper rate I've seen with the D300. One thing I noticed when testing the Sigma 105mm Macro Prime in AI servo mode, the camera wouldn't burst frames at 6 fps. I checked the configurations to make sure the Highlight Tone Priority, Lighting Optimizer, High ISO noise reduction and Auto ISO were disabled, and they were. The camera did fine with 6fps bursts using the 70-200. I'll be exploring this a little more, not quite sure what is going on here.
Highlight Tone Priority and Auto Lighting Optimizer:
Both of these features seem to work as advertised. Most notably, with both enabled, I'm very seldom seeing images that are over/under exposed. The histogram on the raw files is almost always coming up in a close to optimal exposure and it is more likely to overexpose by a 1/3 of a stop than underexpose, which is actually a good thing. No problems making minor exposure compensations to reduce and this actually seems to give an optimal noise performance as well.
Auto ISO:
When enabled, this function is working very well. The camera's program seems to be recognizing the focal length of the lens and not making an ISO adjustment unless the shutter speed/focal length appears to be a poor combination. The camera tries for the lowest usable ISO with optimal shutter speed and I'm fairly pleased with how it handles this. This feature isn't user adjustable as with the Nikon bodies, but I think it is doing a better job of allowing me to turn it on and forget about it. I am always concerned with the D300 as to rather or not it was making a good decision on when to switch ISO and how much. The Nikon seems to want to bump the ISO too high too quickly.
When coupling the Auto ISO/Highlight Tone Priority and Auto Lighting Optimizer, I'm finding that the camera producing very reliable results. This bodes well for wedding and event photography in changing conditions. It takes my mind off of what needs to be changed and makes these changes for me and is doing a good job of it.