Is the cost for a dual 1.8 (they seem pricey still) worth the upgrade if you do have a dual 1.25ghz MDD? I have seen those MDD going for $140 or $125 on LEMswap recently so you have a whole machine with 2GB of RAM for probably around what that CPU upgrade would cost alone. The only dual G4 I have is a Sawtooth with dual 500's (and it runs nicely).

I think the very last G4 tower Apple made was OS 9 bootable, from the looks of it that is where I will stop collecting.