Somebody discovered a new injection issue (:: sigh ::) in 0.5.2, so I put it off slightly. I'll be rolling back that commit and then reposting it hopefully tonight.
These issues are highly personal, and seem to have to do with network connection, cpu speed, etc. Which is why I'm moving Greasemonkey back to a simpler injection system which should be more fool-proof.
Many people are using 0.5.x without trouble (everyone who tested the alphas on the mailing list, for example). For those of you for whom it isn't, I'm not ignoring you. The next version of Greasemonkey should work much better.