Earlier quoted context omitted.
Why do you care about keeping an authentic follower list? I'm honestly curious because I've never really understood this phenomenon.
My main reason is that I don't want to write to an audience of bots. I'm using twitter semi-anonymously so none of my real life friends follow me there (I don't have a separate account for this), so people who follow me and I follow are the people I'd talked to before on twitter. If I'm followed by more bots than actual people, I feel like the social feeling of twitter would fade away. I have a small number of follow…
And I'm definitely a 'tweet deleter' after reading this article[0] and agreeing with the premise that Twitter messages aren't that important to preserve. I'd rather deny data miners the ability to better profile me than keep old messages. The article's linked-to Ruby script to archive & delete messages stopped working recently but I found a newer one[1] which works very well. Set it up as a cron job, set the preferred threshold for RTs, favorites and time, and it keeps your feed tidy. If that old message was so great your followers will mark it as such and the script will preserve it. The rest disappear after X days.
[0]http://fusion.net/story/50322/meet-the-tweet-deleters-people...