Boost your G3 iMac with a G4 processor

Fastmac offers to replace the processor of the slot-loading G3 iMacs with a 500MHz G4 processor. Of course, you will need to send them your motherboard for the installation...
The replacement costs $199, which sorts of dedicates it to die-hard geeks, especially if you consider the graphics card that powers these machines.
[moose: well, it might be a good option for using the old iMac as a server...]