How is "following back" each of the 20,000 people that follow a corporate or prominent blogger account on twitter a legitimate use? Nobody can read that firehose.
It seems like people are overloading the "following" feature --rather than a subscription to the user's content, instead people are using it like a "karma" vote. Maybe they need to separate the two.
I'm sure that if I go through my follower's list I have a lot of people that are twitter "ladies-of-the-night" but I don't follow them so they are not spam to me. I thought that was the whole point of the asymmetric following mechanism. Users choose who they want to be spammed by.
1) The default setting for a long time (not sure about now) was that you'd get an email every time someone new followed you.
2) For those folks looking to make actual social connections on Twitter, it's next to impossible to notice when someone actually interesting starts following you-- the signal-to-noise on the followers lists means that it'll get drowned out. I've had some really interesting leads go stale as a result of this.