There has been a significant change to the Amateur draft in the new Collective Bargaining agreement in MLB. It sets a uniform signing day instead of the former rule of the first day of college classes for the high school draft picks. It also sets up stronger compensation rules for the unsigned draft picks. If a team does not sign there first round pick they will receive that same pick the next year but one pick later in the round. This will affect the signing bonuses of the upcoming draftees. It is very complicated and can be read in further in the Baseball America Article here.