I had read about this and decided to give it a go.
Was in Vegas for the first time a few weeks back.
When checking in (at the Luxor) I folded a $20 between my credit card and drivers license. The guy upgraded me from a standard tower room to a suite. Had a seperate room with a TV, couch, table/chairs, wet bar, etc.
My buddy tried it last week at Excalibur and it worked for him too.