It's overkill for a desktop, but I haven't rebooted in over 15 days.
Linux nerds, don't tell me about your super long uptime home server. This machine sees daily use, sleeps, software updates, etc.
"10:11 up 15 days, 20:24, 2 users, load averages: 0.86 0.72 0.63"
Next upgrade: an SSD of some sort. Probably a hybrid because I don't want to mess with multiple volumes, etc.
If you're in the market for a new desktop, try and find a 2008 Mac Pro desktop. 2006 model is cheaper, but there are a few technical limitations. You can find them with a small warranty on Ebay.
It's super easy to run Windows alongside the Mac with Parallels. Add a second monitor, and you've effectively got two desktop machines.
Backups are easy, the machine never crashes, and they are fast even though they're several years old.
I've gotten over $200 in cash back from them at places I would have shopped anyway! Ebay, Staples, more! I put it at the top because they ROCK. Basically, you get a kickback from Ebates when buy.com or whoever pays them. Win-win. If you like throwing money away, don't use them!