California signed-on with conditions: http://blog.eduflack.com/2009/06/01/what-does-common-standards-mean-to-a-state.aspx
See the actual letter, penned by Gov. Arnold Schwarzenegger, Board of Ed Prez Ted Mitchell, and State Superintendent Jack O’Connell linked on that blog…. No surprise, California seems to believe its current standards are likely the bar by which national standards should be measured, making clear the state “cannot commit to adopting [common standards] until we have determined that they meet or exceed our own.”

Also a great post about common standards, and concerns raised by subject-matter experts are raised on Jay P. Greene’s blog:
http://jaypgreene.com/2009/06/09/the-national-standards-sausage-making/