Windows Live Messenger
I was chatting with a buddy tonight who shall remain anonymous but I was inspired by his IM habits to think up a mod for Messenger:
First, you're allowed to write like 300 chars or something for each message. Anything more and your message gets cropped. So, with my mod, when you hit 50%, the message will change to something like: Adonis Bitar is STILL writing..., it could progress to, Adonis Bitar is not done yet... and so on.
Secondly, I go idle on people all the time and come back several hours later and realize I never completed my thought. Perhaps a message could change to Adonis Bitar has fallen asleep or something...