I think the ram for the Mac Pros is very expensive?
For the models no longer in production. They used fully buffered memory which was not cheap.
However, FB-DIMMs were mainly DDR2, and nobody AFAIK is developing FB for DDR3. The newer models can use standard DDR3 RAM.
My Quad is a good machine. Have to keep it on in the coming winter months, though. I got it for what a 2006 MP costs now, unfortunately, but I'm satisfied with its performance. Just be aware that for a PCIe card being installed it needs to be both OpenFirmware compatible and generally have a PPC driver.
As for my satisfaction? Very high. It satisfies my need for a tower that runs OSX without violating EULAs or mucking about in a legal gray area on-the-cheap with a moderate amount of power. I'll be running it until I upgrade in a few months to an Intel machine. It beats the pants off of the iMacs I used in previous experiences.