I currently use OpenOffice myself, but I'm tiiiiired of it's extremely long startup time and bloat. Java, bleh. Once it's started, it's sorta okay though - but of course I do have a AMD64x2 4400+ w/2gig of ram.
At work we're forced to use MS Office, the alternatives just don't handle the Office file formats well enough... and, well, Office is pretty darn fast compared to OpenOffice, and that's *without* those silly boot-time preloaders.