We held a "$5.00 if you root us" contest at Team Phreak about a year ago, and it was pretty fun to actually see everyone trying different ways of getting into the server.
We haven't planned on doing this again, but now that we don't use that server for anything, maybe I should set it up again.
No one was ever able to break in when we had the contest, or since then. Might be a fun thing to try.