I have run my own mail server for years and I rarely see spam. I'm running a classic Bayesian filter as outlined in the legendary PG post "A Plan For Spam" and it works very well. I don't really get all the fuss about this issue. When I do see a piece of unclassified spam I simply classify it and continue. For me this is a far better tradeoff than having all my most private mail on some bigcorp server where any nerd can rifle through it.