We use OOo. It's better than MS Office in many ways. First, it is just the office suite; it doesn't do any network stuff so there I don't have any security concerns about it. Secondly, it doesn't come with Visual Basic. There is no reason why plain old word processing documents should have visual basic in them. It's just a monstrous security problem to have that. With OpenOffice, I don't need to virus-check files. If I want to, I can look at the XML directly and very easily confirm what the document is and is not doing.
My main hope right now is that all the office suites other than MS Office will standardize to the OOo XML format. That means OOo, KOffice, AbiWord, SoftMaker and WordPerfect should all adopt OOo XML as their default save format. Then we would have real choice and no format lock-in.