Leaving it in one position is an old Brian May thing too.
Using it to subtly accent notes is when it sounds best to me.
I got used to the way the Auto Wah function works in Amplitube so I started trying it on a cry baby and it sounds a lot better the more subtle you are.
The secret is to not overuse it unless you're really into Shaft tunes and porno movies, in which case, go nuts.