Learned the hard way: Windows XP restore on netbook (with broken screen, cheap cheap cheap on Craigslist) requires working primary screen for XP registration. At least I can get a new screen on ebay. And it appears Windows 7 doesn’t have this problem (will find out soon). Linux works, but it’s ugly. Hackintosh would probably work if I could be bothered.
Knew this one already: if you sell a computer on Craigslist, wipe the hard drive first, because you may not sell it to someone as honest as I am. (If you buy a computer on Craigslist, see if there’s anything interesting there before restoring it. Like, say, MP3s, or maybe documents with bank logins!)
Any software you get on a purchased computer, that does not include the original disks, is stolen. And may be virus-infected or configured badly or just plain unnecessary. So pretty much any computer you buy should be restored to factory settings if possible. Windows makes this a royal horrible pain in the tuchas. With OSX it’s simple.