I just ordered 512M of RAM for my PowerBook G4. I find that with only 512M of RAM, it can get extremely slow when I’m compiling something big. Top shows only 5M of free memory when I have lots of stuff running. Unfortunately the current configuration is two 256M DIMMs, so I’ll only have 512M with the upgrade. I will probably replace the other DIMM with a 512M or larger one later.