2003 at work, except for Outlook, they just upgraded it to 2010. OMG it's a bloody pig. I often have to end task and restart it because it just locks up. Especially if I try to work it faster than it can go, such as opening too many emails too fast.
At home I use Libre Office, as it was the default office app when I installed Linux so I stuck with it. I don't use office programs that much though. I have a couple excell spreadsheets to manage my backup rotations (which I should probably put in a web based system anyway) and the odd word document.