I did this last year, so these pictures are a bit old.

It's stable at this speed. I didn't feel like like making the leap to 400 without extensive testing first. (Why yes, I am an engineer) Moving around the resistors is a major pain. One possible mod here would be to install dipswitches. (in theory, that would allow operation from 33MHz to 533MHz) While the processor/heatsink is directly below the fan, I would not be inclined to take this above 400MHz without major modifications to the heatsink. The IBM PPC 750CL is only rated at 333MHz.

Of course, while 333 is fast enough for most purposes, there are some applications that require more. The Digital Archive Project, for example.

CCFL lighting. Since this picture was taken, the plastic endcaps on the tubes have been dremeled down to fit better, and the lights are now parallel to the front. Also, the CCFL driver has been heatshrinked and placed under the motherboard and the on/off switch installed under the usb/ethernet ports. (because sometimes the light does get annoying)

I like the effect from the back.