How to do a diff in Openoffice - and the merge
OpenOffice messed up the style sheets and TOCs in one of my larger documents to the point where I realised the easiest thing would be to merge it into an earlier copy of itself. Now, finding the diff was the easy part: Edit->Compare Document, but what threw me was how to do the merge. Basically I opened the old copy (which would be the new master) and chose to compare it to the new one. Now I was obviously merging into the old document since that one was the one that was open and where I selected Edit->Compare Document, but the merge only happened when I chose to reject all changes. Then the changes were merged in.
Today, I learn from Internet that OpenOffice.org Writer can diff one ODT against another via Edit->Compare Document... :P