Dave Winer has a solution for his e-mail problems. I use a slightly different variation on the same theme.
1) I use a domain that designed for only a few people.
2) E-mail for most any address in the domain is routed to the default account
3) When I give out an e-mail address (either on the web or in person) I give a different version of it. If you are ABC CO then my address will be ABCCO@domain.com.
4) The Variation for webistes is that the address changes fairly frequently and includes a date. If you click a mailto in March 2003 there will be a 0303 in it. If you mail that address after March 2003 you'll get instructions on how to make it a current address. (A very simple challenge-response type system.
This gives me tracking for who is spreading my address. For example a local photo studio recently used the address I'd given them to have photos uploaded to the web to spam me. I sent a nicely worded reply explaining that I would use the fact that they were spamming me in consideration of future business decisions. The apology came in less than an hour and no more spam did.
This won't work for the dedicated spammers and I do still filter spam on the server (using IMAP and pop so that I can filter the messages with a web-based IMAP client and then only download the ones I still want to look at. Squirrel Mail is a great solution for this.