Google thinks spammers might be giving up. The basis is that the spam being sent and received seems to be reaching a lull, at oh, something like 10 billion a day. Filtering and other methods do improve things, but if things are slowing down, I believe it is because it just isn't as lucrative, or other fields are more lucrative. But I don't believe it is slowing down in reality. Probably just become old, not sexy news.