I just posted the following suggestion on Get Satisfaction:
When getting a notification that someone’s following me, it would be nice to see how many people have blocked them. The e-mail notification currently includes how many followers they have, how many tweets they’ve posted, and how many people are following them. However, I’m betting a count of the number of times they’ve been blocked would give the best indication of whether or not that person is in fact a spambot.
I have gotten ten or so follows over the past 24 hours, all from spammers. I block them once I’ve ascertained they are spammy, but the only way to do that is to visit their profile page. A block count might make it easier to filter these spammers out.
If you like this idea, you can head over to Get Satisfaction and throw it a little support. If it gains enough traction, Twitter may notice and actually implement it.