If you go from a miniDV camcorder to your computer via FireWire and back out, you should not see any difference in picture quality (that is if you did cuts only editing). If you edit and add any type of titles or transitions (such as a cross dissolve, or page curl), then there will be some compression applied to your picture. Most of the time this is totally unnoticeable to the naked eye and most people dont worry about it.
Rick Popko
Pinnacle Systems