Any commitment is only until a better offer comes along. Better is a bit loosely defined as there is a cost of burning the bridge with you by jumping (be that a day after accepting or after 5 years of working there), but at the end of the day there this is a business relationship and the extent of our obligations are only spelled out based on any contract we have signed, and our social obligations only extend to the extent that the cost of violating the social obligation outweighs the benefit. Any employee who doesn't see the other side as doing the same is eventually going to get burned by it.