for what it's worth, i just recently bought 1GB (4x246MB) of PC-133 RAM for my B&W G3/350. it was the cheapest crap RAM i could find but even the slowest PC-133 RAM has to be within the spec of PC-100 RAM. it has worked phenomenally well and OS X just flys now.
i'm no expert on RAM, but i do work as an engineer in the semiconductor industry and i have a pretty good idea about how SDRAM works. i don't think you can really go wrong with cheap PC-133 RAM on a 100Mhz system bus.
i wouldn't suggest this cheap stuff for the new 133Mhz bus G4s, but i'm pretty certain that it'll work on the older G4s. it works in my B&W G3 at any rate. of course keep in mind that ALL of the RAM is the same RAM -- i'm not mixing PC-133 and PC-100. keep that in mind.
- j