Dean
in memoriam
For those types of things, alternate communication channels work best for us. Call people up and let them know. Instant messaging, twitter, or even email could work too, but I don't think as well. Problem is, people get into a groove, and it really is tough to get out of that.By announcements I mean "This cool thing is happening, you should check it out" - not "If you post pictures of tubgirl, you'll be shot in the foot"
I would reserve the software tricks for important things like major changes in terms of service.
Although I have seen things done like locking innocent threads (everyone reads locked threads, don't they?) and putting the message at the end... things like that only work 1 or 2 times, and people are generally not happy about that.