I did. Make sure (if you haven't picked a residency yet) that your residency program allows you to do so, if you want to do this. Some residencies have opportunities to moonlight in the same hospitals you do your residency in -- say, in the psych ED -- which is definitely the best way to do it, since you know the system already.
The opportunities and pay vary tremendously from state to state, so you'd have to ask around in your local area.