I use postfix, previously qmail. In both I have address extensions which I use religiously. I use ryand-apple for all my apple stuff and ryand-ruby for all my ruby stuff, etc etc. As a result, I can track where my spam comes from. It turns out, true to the FTC's spam study that very few companies I interact with ever sell my contact information. It's all glommed from the web. specifically, posting to nerd websites or mailing lists that are archived. As a result, most of my spam is to ryand-ruby because I'm active on several lists that are trawled by spammers.
Very clever. It does suffer from the unavoidable flaw that was mentioned above, eventually sites will just stop accepting email addresses that point to that domain. But until that day comes I will be heavily using this service.