I was talking to Gordon Joly and Philafrenzy about this at the Wikimeet and
I think the collective feeling was that contact before and after an editing
session is important as well as the event itself.
I can certainly think of events where lots of people have turned up, but
none of the new wannabe Wikipedians has gone on to contribute after the
event - perhaps this could be improved by some friendly emails afterwards
offering to continue the help offered on the day.
I think we're definitely learning more about how we do these things, and
hopefully these events - whatever form they end up taking - will continue
that.
Chris