Is this a beta program? Am I going to get beta bits that are full of bugs?
No. This is not a beta program. It is a way to get the same bits that the manufacturers get, ahead of whenever your carrier decides to release them. As was demonstrated when this program started, there were those who claimed it was not going to be the final release, and those who claimed it was. As it turned out, those who believed it to be the final release were correct. The build that was given to the Preview for Developers participants was the same build that the manufacturers got from Microsoft. There is no guarantee that this will always be the case, as it is always possible to find a bug and issue a late release, but this definitely is not a beta program. The software being delivered is meant to be ready for prime time.