Funny thing I realized not too long ago is that everyone has a different idea of what it means when they say "I know this person." I used to think sales people were well connected (and I'm sure they are), but when a sales person says they know someone, it probably means they met at a bar somewhere at least once. :)

For myself, it would be hard for me to say I know them, let alone call them up. Maybe the lesson for myself is that most people are pretty receptive of just being called up if you have a legitimate reason and there's no harm in being more open about connecting (you won't get in trouble for calling someone a friend even though they are definition an acquaintance).