"Got the wrong Bob?" is a new Gmail Labs feature aimed to identify when you've accidentally included the wrong person. Based on the groups of people you email most often, Gmail will try to identify wrong person; for e.g. if you normally email Bob Smith together with Tim and Angela, but this time you added Bob Jones instead, Gmail'll warn you that it might be a mistake. Note that this only works if you're emailing more than two people at once. Also changed the name of "Suggest more recipients" to "Don't forget Bob".