For what it's worth, I have both.
Crucial got returned for a bad stick, Mushkin has been fine.
I have 2.5 gig of RAM onboard - 2 Crucial 512's, 2 Mushkin 512's and one Apple 512.
Regarding Mushkin, from what I've read/heard, some PC users have a kind of cult thing
with Mushkin, insisting on it and nothing less.