Dell rebates are usually pretty good compared to other companies - many people get theirs in a month, 6-8 weeks is probably more typical. I think mine came in 6 weeks.
As for OCability - not really. You can raise the FSB via software, but that will raise the PCI and AGP bus speeds as well, which can cause problems. From what I understand, the onboard sound in particular does not like to be out of spec.
As to what you use it for? Uh, what do you use your computer(s) for? Even though it's sold as a server, it has all the goodies of any barebone system you would put together yourself. It has an AGP slot, and is very quiet and runs cool. Like I said in the last thread, if you have spare parts laying around, this is a great deal. If you're going to have to purchase a lot of parts to bring it up to spec, you might want to look at another Dell special, like the 8300 for example.