Then there is SOT office, and StarOffice - all are actually based on StarOffice, which Sun acquired and then opened up (yeah for them).
The StarOffice version still has that funky desktop-like interface thing that no one likes.
I have OO 1.0.1 co-existing with Office XP, and it handles 99% of the stuff. For the easy things (docs & spreadsheets) if you open it in OO, then save it in OO's native format, the file sizes drop considerably.
The only spurs I hit are with some fairly complex scripted spreadsheet "forms" that I make (I'm a bit of an excel guru), but like I said, 99% of the stuff seems pretty darn fine.
Document-matching (layout, etc to original Word) is another story... only about 75% of docs with any kind of advanced formatting (graphics, text boxes, etc) are translated/look correct.
Then again, if the extent of your work is BOLD, Italics, and Underline (plus whatever fonts) it's a great alternative. Keep the "quickstart" option so the thing loads in reasonable time (like MS office uses).
There's several "Free" office suites out there, but OO is basically the best right now. SOT office is fine (pretty much the same) but you need to pay to get updates