The Member Cruises usually do have a mailing that goes out before booking day. As Diana said they announced the 2006 one while we were on the 2005 cruise.
What makes a Member Cruise different than a regular cruise. Well traditionally they have special itineraries. For example the first one did 2 days at CC and Nassau, the 2005 one did Key West, sea day, then CC. The 2006 is doing CC twice with a sea day in between.
Another thing that is different on the Member Cruises is the entertainment and guest speakers. In addition to the wonderful
DCL shows we've also had concerts from Susan Egan and Andrea McArdle. On the last cruise we had Art Linkletter as a guest as well as Ducky Williams.
Last, but by no means least, are the gifts. Every night a different gift. On the first one we got things like
DVC mesh bags, t-shirts, and a limited edition tea pot. On the last one we were welcomed the first day with a huge gift basket. Different pins every night to fit that nights theme, beach towels, and a special Ducky Williams lithograph.
If you want to read about either of the DVC cruises click on the monorailgreen link in my signature and then follow the DVC link. DH and I have been on both of the previous Member Cruises with a great group of DISers and are booked on the 2006 one as well.
Oh yes - one more thing - the DVC Member Cruise has always been a few points higher than a regular 4 day cruise at the same time frame. Some don't find the value in that but we always have felt the extras mentioned above have made it worth it.