Another interesting comment — it’s funny, but may also contain some truth in it. In any cases – spam suck.

Quoted from comment #16672295 :

Right now, spam goes past spam filters by including a large amount of random nonsense text that resembles English language reasonably well. So we will get spam filters that detect large amounts of random nonsense text. So spam will include text that makes actual sense. Give it twenty years, and your average spam email will consist of 300 pages of text that is better than anything Shakespeare has ever written, followed by two lines begging you to buy viagra. Thirty years, spam will be two hour Quicktime movies better than anything you can watch in the cinema today, with the hero using viagra bought from the spammer in the right places.

Anyway, the real solution to stop spam is to use multi-tiered filtering system.

Bayesian filter, captcha, blacklists, user-submission etc are no longer effective when used on their own. But when combined (example: SpamAssassin, Spam Karma 2), their effectiveness will goes up surprisingly high.

You’ll need to pay attention on the order of deployment though — incoming email should be received by the blacklist filter first. This will cut the number of spam tremendously, so other filtering engines (which are also more resource-hungry) won’t be overwhelmed / won’t overwhelm the server they’re on.
User-submission (example: razor) should be last, you don’t want to annoy your users too much really.