I kind of think this repair permissions / update prebindings stuff is an old wives' tale.

I've been using MacOSX heavily every day since pre-launch back in 2000 or whatever, have worked with thousands of Macs, and I've never once done it. Never experienced a problem that it would have solved.

I think the only case in which it's actually necessary is when a partially-failed version upgrade or incomplete install left something inconsistent.