Gnome-terminal activity notifications
There is a terminal application for Mac OS X called iTerm. It's pretty excellent. If you're using Mac OS X, this is the terminal to use. It's got tabs and transparency and all the good, modern stuff.
But if you're a real person like me, you use Linux, and you use gnome-terminal. Or, I'll concede, you might use Konsole.
These programs each lack a feature present in iTerm that I happen to like a lot. In iTerm, if you are on tab A, and output is generated on tab B, the title text for tab B turns purple. After a couple of seconds with no output, the text turns red. When you switch to that tab, the text turns black again.
I like this a lot. It means that I can run a compilation in one tab and be notified when it ends, even if I forget to add "; beep" or something to the command-line (I always forget to do that).
Someone should do something about that.