Suggestions to detect spam

Spam filters have been losing ground lately. I use an Yahoo! account and every day I get more and more undetected spam in my inbox. The Bayesian filter doesn't seem to be detecting all of them.

So here are my 2 cents:

- If the message that just arrived is old (3 months or older), it's spam. Trust me on this one.

- If the message only contains a stupid inline image, it's also spam.

I don't understand spam. I don't know who in their right mind would buy anything being advertised in an e-mail that starts with these lines:

Rocks appearing show series remarks by, sex.
Mentioned being member, brat. Bald failed box office garnered mixed
nude pregnancy famous.

Seriously. How stupid do you have to be?