Yes, if you're used to using the same OS every day but on a MacBook Pro, then of course on the G3 it will feel slow, just like if you drive a Ferrari every day and then try a BMW 330 it will feel slow in comparison to what you're used to, despite being anything but. OS X feels fast on the G3 to me as I don't have any newer Macs (though I did find that the music videos in iTunes (the previews of the ones you can buy) don't seem to play properly). I wouldn't install Jaguar unless you have an extremely small amount of Ram and cannot upgrade it, as if you have plenty of Ram the newer ones will be faster. You don't need to upgrade the CPU to a 1GHz G4, and Ram is cheap - the G3 is fast enough unless you want to use lots of heavy-duty AltiVec-enabled apps (non-AltiVec apps won't see a big speed increase going from G3 to G4 unless you get a much higher clock speed).