I have some bad experience with PC ram before. It's an elcheapo notebook ram that works fine on a Wintel laptop. But when I clonk it in my iBook... it will never awaken from it's 'sleep'. Have to force restart everytime. Come to think of it, ever since I bought my iBook, during those few days are the only time I experience kernel panic with OsX.
Take out the offending ram solves everything, but it's unbearably slow running OsX WITH 128MB, so I just went ahead and buy an Apple 256mb ram. It's been smooth sailing eversince.
Maybe it's due to the extremely elcheapo ram I use, but lots of Mac users been having a terriffic experience with Crucial.
Note: The spec of the ram is right, PC100 and so on...