I purchased a Mac Pro 1.1 last summer for $1200. It came with a 23" cinema display that I sold for $300. It also has the dual 4 core 3.0ghz upgrade (x5365s), 32 gigs of ram, a 5770, and twin 500gig hard drives. I updated the firmware to 2.1, and upgraded the main HD to be a 128 gig SSD. I use it for CAD modeling and rendering, some of my renders and animations take DAYS, and they're using 100% of all 8 cores.
Sure, it's from 2007, but it will take a mini outside, place it's teeth on the curb, and stomp its skull inside out. If you're doing an intensive process that doesn' use all 8 cores, the machine is still usable. It's quiet, stable, and I think it's great. The only thing that sucks is the EFI isn't 64 bit, and I can't run the newest graphics cards.
Sure, it's from 2007, but it will take a mini outside, place it's teeth on the curb, and stomp its skull inside out. If you're doing an intensive process that doesn' use all 8 cores, the machine is still usable. It's quiet, stable, and I think it's great. The only thing that sucks is the EFI isn't 64 bit, and I can't run the newest graphics cards.