I've noticed a common spam method lately, which I'm not quite sure what the idea is since it is so obviously spam, and trivially filterable that it doesn't seem like it will last very long, but a couple have ended up in my inbox, and since I really don't like emails in my inbox I decided I would write a filter to keep this type out.

:0:
* ^From:[^@]+@[^@]+@
spam/mail

Pretty simple - just look for multiple @ signs in the From address - I can't think of a reason why someone would do that on purpose.  Though maybe some people have "joe@example.com" <joe@example.com> as their from address - I'll have to see if it results in any false positives.