CIDOC has a Bulletin Board for discussion of topics of relevance: see the CIDOC Forum.
There is a CIDOC LinkedIn group, which you may join if you are a LinkedIn member: www.linkedin.com.
While CIDOC does not currently have its own presence on photographic sites, you can use keywords to flag your comments, photographs, etc. on services such as Flickr, Picasa or Facebook. For CIDOC Conferences, just use "cidoc" followed by the year, e.g. "cidoc2009" for the Santiago Conference. (You will find some photos on Flickr under this keyword.)