My computer is real slow, and when I want to do things like rake a rails app or compile something, it takes awhile, and I always forget what was doing. But not if I can have some sort of alarm go off whenever the terminal finishes it's current task:

alias beep="echo -en \"\\007\""

Bingo! Then just clip it onto the end of a command, and when that command finishes, the terminal should beep (\007 is a character code that should make a sound when it's echoed).

rake;beep

And rake can run all the tests I've written for a rails app, and give me a yell when it finishes.