I don't use it. It eats up too much of my RAM.
Occasionally, when I am bored, I'll pop it open and use a CPU meter for dual core CPU, a RAM usage monitor, a local weather app. I forget what else.
It's sad. I have 2 gigs of RAM, and idle my machine uses 25% of it, usually 30 to 35% with Firefox, and maybe only 90% with even the most intensive games, yet I feel like I never have enough.