For all of you tweeters out there, Twitter Moms has a PPD support group going that's pretty interesting. It doesn't seem super active, but there are about 30 great moms in the group who are hitting some important PPD topics.
While there, you can listen to a podcast by Dr. Heather, who calls herself the "babyshrink." You can also enter a discussion forum and contribute to topics such as "When did you realize it was PPD?" There is venting going on as well as sharing. But, most importantly, moms can easily connect to other moms who are dealing with a postpartum mood disorder by simply clicking on their photo.