+1 on check your local laws since you didn't provide a location. Around here it is technically illegal to dumpster dive, and Milwaukee passed an ordinance against snagging stuff off the curb on trash days. A free bike ain't free if you get a $50-$500 ticket and have to return the bike to where you found it.

As to the Buffet dumpster, if it moves it ain't rice. Heard that in Seattle once, one homeless guy talking to another as I was wandering around taking pictures in the city.