I purchased my 512 stick for my iBook G4 from Crucial as well. It is is a bit more expensive (but only ~$10) but you get a good warrenty, excellent customer service, super fast free shipping, and if you use their RAM selector you are guareenteed to get compatable RAM or they replace it.
When I ordered the RAM for my iBook, I also ordered RAM for my FH's PC. He thought about getting a faster speed and they told me that if he wanted to swap the RAM, I could pay the difference and they would send me (via 2 day air) a return ship. They would ship the new RAM the day they registered the old RAM coming back.