Most of the time it is called leasing. You can be successful doing them, but you need to have a good contract written up. I had a lease all set up for bestwineclub.com but my leasee backed out at the last minute.
I suppose its an alright idea...however what if you are the leasee and lease from say, Mr X - if your site became "huge" Mr X may take it upon himself to take over and clame it as his.