I just got finished reading Education Sector's very interesting report on teachers' opinion about their unions. I found it enlightening and distressing in turns. For example, the teachers surveyed feel strongly that they need unions to protect them from capricious administrators; therefore, teachers want unions to stay focused on pay, work conditions, job security, etc.
While there are differences between newer and more veteran teachers, their views are more similar than I would have guessed, and those views aren't so encouraging for those interested in changing the teaching profession.
These are just a few of the fascinating findings; if you have 15 minutes, take a look.
Along these lines, Education Sector just launched an online discussion with teachers to debate the future of teacher unions. Also worth browsing.