Yeah, I totally agree that it's often management more than numbers that affect balance, since I've known groups with the same or more members that give each member screen time better than some mid-size groups, and some small-size groups with only like one member who gets any attention.

I still use twitter because it's often useful for getting information fast and for short, quick interactions, but I used tumblr for like a year and then got totally bored with it because the level of interaction amongst users seemed so super low. And it felt really disorganized sometimes too. On lj, it's so much easier to actually get to know a person (if they're at least somewhat active).