I know I said no feature requests, but I need to bookmark this idea for
my own future use, so:

dmarti suggests "in an email client, next to a
person's name, display a sparkline showing times of day when that
person has sent you mail, with a vertical line indicating the current
time."

http://www.linuxworld.com/community/?q=node/712

I'm thinking
this might be useful (perhaps a day-of-week thing too/instead) for
gamemasters to see, in particular.