I didn't see it mentioned above, so I'll mention this one detail regarding Powergrips.

The metal piece which extends from side to hold the strap open wide enough for regular shoes will strike the ground in tight turns if you're using on a road bike (or any bike with a low BB). I had pedal strikes with PGs on my LHT on the very first ride, where pedals alone never struck the ground before in thousands of rides. I had to stop pedaling through some turns to prevent this. I gave up on the PGs pretty quickly for this reason.

http://biketouringnews.com/wp-conten...ergrip-007.jpg

PGs do hold your foot in place, however getting into them is harder than toe clips. I prefer toe clips to PGs overall.