I like openoffice. I used it for years until my employer paid for an employee purchase plan for the office suite we use at work, which lets me buy a single user license of office for $20. I guess letting people use office at home is cheaper than having to train everyone up at work...
I've tried a bunch of other free office-like suites, and open office was my favorite. One thing though, it isn't a "free version of MS office". It's completely different, duplicating many of the features of office and attempting to reverse-engineer some of the proprietary stuff in MS office such as their closed document formatting standards. Ironically, the success of open office forced MS to start offering open-source document formatting standards several years ago, when saving MS office documents.
No reason to not use open office, unless you are sharing documents that have complicated formatting with people who have MS Office and who don't know how to select compatible formatting standards.