Being a Mac person I'm well aware of the liquid cooled G5 (especially the quad

) but I've never owned one. Though a few months ago I was playing around with an HP workstation and was surprised to find HP made a liquid cooling system that could be installed in place of the standard heatsinks and fans and it takes about 5 mins to install.
That got me wondering about other systems that came with stock liquid cooling. I'm thinking more desktop/servers than huge supercomputers with liquid-cooled doors

but post anything that you think is interesting.
Apple Power Macintosh G5 Info from everymac.com.2x 2.5 GHz G5 (2004)
2x 2.7 GHz G5 (Early 2005)
2x 2.5 GHz dual-core (Late 2005)
HP XW9400 -
HP Datasheet PDFDual Opteron workstation based on a slightly modified Tyan S2915 motherboard. Liquid cooling was an option on higher spec'ed models and since the water blocks, pump, and radiator are all a single unit, it can be added to any system. With a BIOS update 2.8 GHz six-core Istanbul Opterons are supported.
I had the HP maxed out with twelve 2.8 GHz cores and the liquid cooling system but downgraded it to the original dual-core processors when I bought my Mac Pro and put the standard heatsinks back in. Here's some shots of the cooling system. The radiator replaces a large rear case fan and the rest of the unit sits over the processors. I never did any serious testing of temp control and noise though the system was quiet and the CPU temps around 55-65 C under 100% load for hours.