I ran into so many compatibility problems I could barely believe it. Couldn't edit each other's headers, no maths support worked between the two, images and other objects would get randomly shuffled in the documents (one image showing up where another used to be). To say nothing of the minor niggling display differences reminiscent of the old IE6 box model problems.

I had to start sending documents in PDF, but then they couldn't edit them. That alone was enough to move me back to Windows.

For better or worse, I don't think Libreoffice can move forward until interoperability can be presumed.