Nice! Glad to see the scripts coming to some use and being generalized that nicely.(did you happen to find the thread because you saw me looking at it earlier today?)
I just recently picked up Greasemonkey again, for an April's fools at work. We spent a day coming up with different gags and implementing one. We decided to make fun of a co-worker who is a bit paranoid when it comes to being spied on online.
The script we made adds a message to Google, about the "Google University Employee Supervision Initiative". About 20% of all search results where censored when moused over. When you confirmed or denied your identity, you got a weird message about the Stockholm University supervision task force
coming to see you.
The actual name and area of research removed in example:
Needless to say he was pretty freaked out for the first few hours of the day. By the time we got there he had figured it out and was pretty pissed off (and very impressed)