I like the fruit fly thing. Also rotating avatars. Using both.
Since one of my forums is new and don't get a lot of traffic, I didn't want to skew the page figuring they will never come back.
People rely on forums. Making them completely unusable, even for one day doesn't make sense to me.
Or you can install the add-on I made in 1 minute and avoid any template edits.
I'm toying with the users on one of client sites and I enable/disable the add-on at random times so they wonder what is going on, LOL.