I have noticed a couple things with my XBOX360 and IR control. The power button / IR command will always turn it off when pressed, but only turns it on if you used IR to power it down the last time you turned it off. If you used the controller or a hard button press to shut it down, the only button I can use to power it up is the code from the Media Center button from the white Microsoft supplied remote.

I'm not sure if this has changed with the XBOX360 slim or not.... One other small thing I noticed. After I power it up via IR, the "right" command on the jog control for will not function until you press one of the other directions first.... I can see the code is being sent, so that's an XBOX thing.