I must must be missing something but I do not see how you could add social bookmarking sites such as some of the more popular ones like digg, Google Bookmarks, reddit etc to BMD4. After research it seems the best way to get the most out of BMD4 is to add your own SB sites. If this is possible please explain.
I don't have that software to explain you the steps but it is not very hard. I guess all the software have help manual pages along with it. Just read it and if you are still not able to get it. You can contact the BMD support here
I see that you can you can Scuttle and Pligg sites to it. But I also see a few well known SB's like faves, delicious etc. I will contact support about this.
I contacted their support and they stated you will not be able to add the popular SB sites. Then did mention Digg will be part of the upgrade though.
The new version ( Version 5.4 ) has this ability. Buy it and add your desired social bookmarking websites to it.