I've used OOO since ver 1 and the versions the past couple of years give very few, if any format errors when loading/saving m$ docs afaik.
I'm in the same area as you, and noticed that once OO was doing superbly on translating the documents, MS went .docx and small issues started sprouting up again. Granted, I'm at the point where I rarely if ever even use office, but I do save in .doc format a lot just to be able to email things to other ppl for their own reading. I find the bigger issues arise when you have a very graphics intensive layout, or try wonky spacing techniques (i.e., my wife - master of the thirty space-bar word shuffle).