I did once in my last job, because we were told AWS was sunning down SimpleDB. We were able to swap to DynamoDB with relatively little fuss (though obviously not none, no migration is entirely painless) because we abstracted it so well. Turns out that several years later, SimpleDB is still up and running, but it was probably a good migration anyway.

Probably a bigger benefit though, is being able to use a different DB in production (probably big scale) vs on your personal machine while developing.