I run several twitterbots. The ones that autofollow back used to attract large numbers of spammers (until I fixed that). The others don't. I guess the usual spam strategy is "follow - wait a few days for reciprocation - leave if it doesn't happen". So the amount of Twitter spam you see probably depends on your willingness to follow back anyone and everyone just because they follow you.
Interesting. I don't "follow back" at all, because I turned off notification of when people are following me. I follow people who say interesting things that land on my radar, and that's it.
I have found on twitter that spammers come after me after I tweet something @ a high profile tweeter. Perhaps this is a factor in the differences in your experiences.
that's interesting that you don't see spam on twitter. i stopped having follower emails sent to me, because so many new followers were spam.
the @reply spam is unavoidable, but rare enough that it's just mildly annoying, not a serious issue for me.