Twitter could still use such obvious discrepencies (and does, I believe) to nuke spam accounts without the numbers being publicly visible.

But it's the non-obvious discrepancies that I'm more concerned with. I have no qualms about blocking people when their following/follower ratio is off-kilter.

You could just look at their last 5 posts. Even if it is a bot that only shoots out links, if you are interested in those links, it shouldn't matter what their numbers are.

It is? How about you follow people you know or people who say interesting things. Or does that just make too much sense? ;)

It's more a question of who I block. Sometimes I have IRL friends who sign up for twitter and have no tweets yet. If I see that they also have 10000 people they are following, I don't waste time figuring out if I know them.

Every spam account I've seen has had several hundred followers.

Mostly other spambots, I'm sure, or other karma/attention-whores, but the point is that follower ratio isn't a very good metric.