I think this is a fantastic idea, but the filter could stand to benefit from better requirements. For example number of direct messages sent to the user (since people don't DM spam bots very often), number of @replies sent to the user.
It could stand to happen that a lot of users who use sites like Brightkite or other sites where they broadcast what they're listening to or where they're at could get caught u p in your spam/bot filter simply for making heavier use of such sites.
I'd revisit your filter to look at how the user interacts with other users, versus just monitoring posting behavior.
You made some very good points. But we also take into consideration the number of followers, so if sites like slashdot or Brightkite broadcast their info and have lots of followers, the spam count will go down too.
Lots of variables in there and I plan to improve even more.
It could stand to happen that a lot of users who use sites like Brightkite or other sites where they broadcast what they're listening to or where they're at could get caught u p in your spam/bot filter simply for making heavier use of such sites.
I'd revisit your filter to look at how the user interacts with other users, versus just monitoring posting behavior.