I think this is the one thing I feel BitKeeper does better than Git. Git can get confused about where a file came from, for moves but especially for copies, and so the version history ends, even if you ask it to try and follow along. BitKeeper, on the other hand, keeps the moves and copies as part of the history, so you can always trace it through to the origin of the file, no matter how circuitous.

git log has --follow but unfortunately it only works when spefying a single file and not e.g. a whole directory.