My ISP does a decent job of filtering. In addition, I have a Spamcop address, which I use for anybody that isn't in my address book (like online orders or posts to web-based forums).
The ISP routinely blocks about 100 spams per day. Any spam that sneaks through gets reported to Spamcop, with a copy sent to my ISP's special "block this from now on" address. I can only hope that they don't just block that particular address, but also do some pattern checking. I'm not confident that they do, but still, it beats 100 spams per day (usually I get no more than 5 or so per day - sometimes none at all).
"When once you have tasted flight, you will forever walk the Earth with your eyes turned skyward, for here you have been, and there you will always long to return."
--Leonardo da Vinci