I have been using Open Office myself, exclusively, for more than 3 years now. The wife had built me a new system, and during the installation process I decided I would, for security reasons, abandon every piece of Microsoft software that I could get away from. I shifted my browser and e-mail client to Mozilla, and rather than installing Microsoft Office, I installed Open Office.
There were no transition issues. Open Office opens MS Office documents with very few problems, and saves documents in MS Office format if I need it to; however, I have been transitioning all my current files into open document formats, so the need to convert to MS Office format almost never occurs. If I need to send a document to someone else, there is a "convert to PDF" button right on the the main menu bar, making the process of creating a shared document completely painless. The interface is quite intuitive, and similar enough to MS Office programs to make general usage by those familiar with MS Office quite painless.
The wife dabbles in computer repair in addition to her day job. As her one and only flunky, I get to do most of the grunt work installations that go along with recovering systems that have been turned into zombies or spambots. In addition to installing Mozilla to handle internet and mail, I add Open Office to those systems that don't have a valid copy of MS Office. I have never gotten a complaint resulting from this practice.
Here's the best part, though. Since Open Office is an open source project, I did not have to pay a massive fee for the software, before I was even certain that I would find it useful. This is the Achilles heal of corporate software, in my experience. If I want to test new software, I am forced to either gamble my money on untested software, or I have to pirate a copy of it for testing purposes. Neither of those options are comfortable options for me, so I'm glad I have the option to simply download and install software without the intrusive licensing restrictions, and to contribute to those software ventures that I find useful.
I would like to thank the Open Office team for their dedication to OpenOffice.org.