For background information, please see the annotation overview on the W3C collaboration overview.
Please see the W3C Annotation Working Group web site, which is kept actively up-to-date by Wayne Gramlich.
If you would like to participate in the Annotation working group, please send a statement of interest to the chair, Wayne Gramlich.
The Annotation working group discussion currently takes places over the w3c-collab-annotation mailing list. If you are a member of the working group, you can review the mailing list archives.