The only issue I found is that you have to be careful not to take out the CF card too quickly after opening the CF card door (like wait 2-3 seconds) or it will drain your battery.
I think I remember reading this in their info now that you bring it up. I was just about to buy a new battery for my 50D but I'll try charging/storing one more time because I was most definitely yanking the card immediately after turning off. Thanks for the reminder!
As for ML with respect to Canon warranty, according to US law, Canon cannot refuse to warranty the camera just because the 3rd party soft was installed. They can only refuse to warranty if they can show the 3rd party soft caused the problem.
So, for example, if you have a mechanical problem with a button or knob or whatever, Canon cannot refuse to warranty according to US law just because you installed ML, or even if you send it to them with ML installed.
Of course this is according to US law, not according to the economics of going after them
in the legal system when they refuse to warranty in contradtiction to US law.