With Android it's pretty much not needed. It's a pretty rare occasion (I can't say it's every happened with my G1 or MyTouch, so...) when simply holding the power button won't give you the power-down menu, no matter what kind of crazy things an application has done. If things get really bad (a deep down error in the OS... also a very rare occasion) it will more likely reboot itself than simply freeze up.
But if that rare occasion does happen, you'll just pop off the back cover and pull out the battery for a few seconds. No harm, no foul.
Started with an AT&T Tilt. Loved it, until I met a darling little 'droid...
Now: Nexus One!
I salute you, old fella MyTouch.