A question for those who have used both:
Tell the truth.
If you could use only one,
and Bill Gates gave you a free copy of the latest Microsoft Office,
which would you use:
Open Office or Microsoft Office?
As a university person, Microsoft Office * is * free for us - with the
department's copy for educational use. Even if I go to buy it, it's only
something like $30 after all discounts.
So I think I'm in an excellent position to answer your question

Especially when you consider how extensively I use office applications.
Although I used to regularly use MS Office, I haven't even had an
installation of Microsoft Office on my system for over a year. This is
despite completing a thesis, editing legal documents for interchange with
law firms, exchanging business documents, and writing academic papers for
publishing as well as presentations to be given off of the computer. On top
of that I also extensively use spreadsheets for business operations.
I have NOT needed MS Office to do any of these things. OpenOffice.org is
adequate - it has all the essential features, including the essential style
list tools for real publishing, document comparison capabilities and
import/export abilities, a capable spreadsheet, and a presentation program
that does its job while interoperating with PowerPoint.
But it's not just that OpenOffice.org is "adequate" for the job. When I
consider everything, I think OpenOffice.org is superior in several
important respects. As a software developer, I recognize these important
aspects and hope that others can understand the rationale here too:
- OpenOffice.org runs on multiple platforms. Currently: Windows, Linux,
Solaris, FreeBSD, Mac OS X. This is important because I do use several
operating systems, including heavy Linux use. It is a huge advantage for me
to be able to work on the same documents with the same interface whether I
have booted Linux, Windows, or whether I am at the university where Solaris
installations are everywhere.
- OpenOffice.org is stable, and runs smoothly. It has not crashed on me
under Windows or Linux, and does not do wacky things. MS Word has scared me
in the past with some of its flaky behaviour.
- I trust the OpenOffice.org software and its developers. It's open source,
and the Internet community is heavily involved with improving Sun's
original software. Remember when millions of MS Office installations seized
up (think it was a couple years ago) because of license expiry/update
issues? You don't get that kind of hassle with open source software.
- Data longevity: this is an important one, and often overlooked because
it's about the future. Microsoft has made it clear that it wants
proprietary document formats. That works, as long as Microsoft is around
and developing software to read your old files. Personally, I'm more
comfortable with my OpenOffice.org documents in XML format because I know
that in the worst case scenario, I can unzip the document structure and
easily extract text from the XML components. This is technical, but what it
comes down to is: my data is easily accessible in the future.
- Data interchange: this builds on the previous point. MS uses proprietary
document formats and is unwilling to make data flow smoothly between
different software from independent vendors. It's just not in their best
interest. OpenOffice.org uses data formats designed to be easily
interchanged, and other projects are cooperating with the vision of open
document interchange - e.g. Abiword.
Now, given the rapid worldwide growth in popularity of open source
software, including OpenOffice.org, do you really think you're better off
locking your documents into an inflexible, non-exchangeable format (MS Word
version X). I would argue that for anyone who values document longevity and
interchange, it's in their best interest to use software with open data
formats.
After all: software companies die, but information lasts forever.