The SOA Manifesto signatories page went live a few days ago. Approximately 300 people have already signed up to show their support for the Manifesto, including some very well known names, and some of the worlds leading corporations and organizations. You can see a list of the signatories here.
In addition, Thomas Erl has very eloquently described the background and the process that lead to the Manifesto, you can read that here.
Lastly, if you read the SOA Manifesto, and agree with the value statements and principles it sets forth, you can show your support and become a signatory here.