Re: For me it's older Xeon workstations.
Yes, I got one (dual quad-core 3GHz with 8GB RAM for £185) and very nice it is too. However, there is a strange problem with many T5400 motherbords (which happened in mine after three months regular use) in that they can develop a fault where on restart, but before booting from the HD, they hang up with just a flashing cursor showing for 5 minutes before proceeding to start up as normal. After trying three replacement motherboards from a local PC-recycler-seller, I found that this was a common problem. I won't go into details but I think it's caused by repeated mains power cycling, which is the sort of thing you do when you get a second hand machine and start fitting bits to it and generally messing around with it. In 'normal' use in a commercial environment, this doesn't happen to them.
I've seen reports of problems with an identical description on various forums.