Well, it uses it up like all electrical connections, but other than wearing out the switch after 10 years or so, nothing bad happens, as far as I know; I could be wrong about that, but I'm fairly certain I'm not. I've been using computers since a little before my first birthday (I have video of it, no lie; even I didn't know 'till I saw it), and of all the many problems I've had, the power switch isn't one of them.
Weeellll, except on the E-Machine. But that's different.