A previous company adopted OpenOffice for all internal uses, and our employees quickly came to love it. We had a customer once who sent us particularly tricky documents, and eventually we gave up and started using Word to manage their stuff. They still complained at broken formatting after we'd edited their docs and mailed them back, though. The conversation went like:

Us: That's really strange. We were using a different word processor, but you're still seeing the same problems even after we went back to Word.

Them: Um, what word processor would that be?

Us: You probably haven't heard of it, but OpenOffice.

Them: Us too! Can we just send you ODT files directly?

The workflow on both ends had been to work natively in Writer, then export to .doc for passing files around. All problems immediately went away once we dropped the middle step.