I have a stream to follow our corporate executives, one to follow my management chain, and one to follow blogs that I like. Aside from that, I tend to follow places and content rather than people because the results are more topical. A chatty person might have valuable things to say in some places but I don't necessarily want to see all their social discussions cluttering up my activity stream.
We also have Popular Content and Unanswered Questions widgets on our home page so I look at those from time to time for things that I might not see in my activity streams. And users have learned the power of @mentioning so I will often get pulled into discussions I wasn't previously aware of. Finally, I'm lucky enough to not have to be the sole admin of our community. I co-manage it with Laura Becraft so having two sets of eyes means that often one of us will see something that the other one doesn't and share it.