I am a great fan of Connections Blogs and Activities.  I use an Activitiy to manage the QA portion of our Connections deployment (currently on 2.5).  This Activity bacame so large the performance became very bad taking minutes to just open.  This got so big because I was able to pull people in by using the "Notify Others" function.  I also use this in Blogs to notify other that may be interested in mine, or someone else's blog post.  We are still stuck in email and we need to use email to get people out of email.  I would like to see a function to notify specific people within a Community of a specific Topic Post, similar to Blogs and Activities.