A very good question I've been asking myself and here's what I've come up with:

If I were to build a simple social network enviroment, that required no interactions with other parts of my site, I would need ActiveSocial.

If I were to build a flexible social network enviroment that also interacts with various other parts of my site, I would need SmartSocial.

I my situation, I need a flexible social network enviroment that will interact between modules and data/content. I don't feel confident I have the same ability with ActiveSocial. Sure the UI looks good but once my users are past that, it's the interaction between the modules and content that will make them come back. Maybe it's just that I haven't seen a site fully integrate - integrate, not overtake - ActiveSocial yet.

The only thing ActiveSocial really offers here and now is that great forum module. It's too bad and basically I think is bad for the dnn community in general, this wonderful forum doesn't fully interact with modules like SmartSocial or Venexus. Anyone releasing a forum module doing just that, would find buckets of gold under that rock.

This is definitely an interesting perspective, but not entirely accurate.  We found that many of our Active Forums Customers wanted a unified social networking solution.  Many of them had tried to piece together a solution by adding several different modules.  They were not happy with results.  Active Social will integrate with other products and content where it makes the most sense.  Not only where it makes sense, but also where it is transparent to the end user.