I’m a member of a blogger community and we did a digg group for example to help each other out.
Usually it is you who submit your article first to these bookmarking services.
The group members can then read, comment, etc your submissions, and if it is valuable for them, they will likely to give it another digg/prop/etc than people who don’t know you.
It is a win-win situation, because you digg other’s stories, and they digg yours – social bookmarking can only be played for its best potential with big network of people in your friends list. Of course spamming is not tolerated, you cannot shout to others to digg your one word article, but it definitely works, I got quality traffic from digg or propeller for example, stumbleupon is not that good for me, maybe because I don’t have many friends there yet.
I wonder that CAP is a great community, why we don’t do a similar community like this one I’m member of and help each other out?