Finally, someone has created a PID tunning howto video, from scratch to perfect stabilize flight, that I think will be very useful for the arducopter community, specially for those flying non stock frames.
The concepts are already in the AC2 PID tweaking guide developed by Jason, but a visual howto helps a lot!
First, acro mode tunning (which I always discard, but I'm realizing it is pretty relevant):
Second, stable mode tunning:
The full post with Menno comments is here.
If the arducopter developers think it is useful maybe it could be added to the wiki (with Menno permission obviously).