I had a look at a really old thread (the reviews thread for Karsten's "Bart Wars: When Dark Lords Attack", in fact. Still a really good fic!), and was entertained by the following edit notice at the bottom of one of my posts:
« Last Edit: January 01, 1970, 01:00:00 AM by 1046408400 »
In fact, a lot of the posts in that thread seem to have been edited at the same date. I assume this is some sort of auto-reset feature, but it's brilliant nevertheless.