It is an open group on Facebook titled TAST 2012
Also as of this morning we have 428 people with a web presence signed on to take on this challenge. It is really going to be a lot of fun.
Further information on the FAQ page
If you need further information on the challenge a list of stitches covered so far or directions on how to participate please visit the TAST FAQ page.
You can read back through TAST articles by browsing Challenges - Take a Stitch Tuesday category
Other groups and networks
You can also share your explorations with other members on the social network site of your choice. There is a Facebook TAST 2012 page, stitchin fingers group and the flickr TAST site. These sub groups are set up by the request of members you do not have join any of them.