The reason I say you may want to convert everything to MP4 at some point or another is because this is the format used by the iPad, iPhone, AppleTV, most third-party streaming video solutions (slingbox for example), and it's a very widely-accepted standard etc.

It's a PITA having video in other formats, because they work with this but they don't work with that, and so forth. I used to burn all my DivX AVIs to disc and play them on my DVD player (which supported the format), but eventually the AppleTV was just a much better idea.