Join some groups and toss some of your pics into them. Participate in some of the discussions in those groups, just like on DPC. I'd suggest finding a group for your local area first. The real power of Flickr to me is all the specialty user groups for whatever equipment and software you use. As much good help as I get from DPC, if I have a question about PaintShop Pro, I will go to the Flickr group for it first. There are also groups for various styles and types of imagery (I'll bet you can find a group for "tied up beefcake", or something like that). Here are a few of the groups I belong to, just to give you an idea of what is available:
I also like the portrait group. Even though the quality is often worse than the strobist group, there are still plenty of good images and it's large enough that you should get views and comments on images you post there.
Your photostream is pretty much the same thing as your portfolio is on DPC.
Once you have a bunch of DPC people in your Flickr contacts, you'll need to be careful about posting your challenge entries over there while they are in voting. Your homepage will show you recent uploads from your contacts and I have some times had a challenge entry inadvertently revealed to me because I saw it there.
