I don't have a whole lot to add to what other people have said. The difficulties in using LyX for cross-program collaboration will depend very much upon your field. I wrote a paper a while back with someone who was using Word, or maybe even an old version of WordPerfect, but it was relatively painless, because there was almost no technical material in it. So I was able to export to RTF, he could do what he wanted and send it back marked with his changes in blue, and I could put those changes back into LyX. For our next paper, though, I was able to get him to use LyX.
I've also managed to get several of my students using LyX. It takes time for them to adjust to a new way of working. But once they adjust, they are all very glad that they have. The problem, of course, is that people tend not to realize that there even could be another way of working, or that it might have real benefits. You don't realize until you stop using Word, etc, how much the program gets in the way of just writing. It sounds almost crazy, but it's true.
Richard
