In a past post I suggested some social tools designed where each task object has a conversation stream. The task object itself can have comments, but also a forum or blog post may be tagged with the object ID, so when you look at the object, not only do you see it’s own comment stream, you also see blog and forum posts that refer to it (kind of like a trackback). I believe both Traction and Basecamp do something similar to what I just explained.