I'm still using XP on the family's computers because replacing XP would take effort, and there is no real reason to do so yet. My own personal computers all run Debian.
Same here - well Mint, but yeah. It's not just that XP is adequate, it's that MS Office 2003 (I think?) which works fine on XP, is adequate. The last big upgrades were from IE to Chrome, and Outlook Express to MS Live Mail. The former at my suggestion, and the latter because OE was developing serious issues with a gigantic inbox.
At the end of the day though, reinstalling Mint takes about 20 minutes, whereas reinstalling XP on a new drive took a couple of days what with upgrades, drivers etc.