Subject lines for emails should be required to have only words that can be found in the dictionary. This eliminates any spam like vi@gr@ or m0rtgage.
The real problem isn't from companies who send bulk email and allow you to opt out. The problem comes from people that are trying not to let you opt out. Not only don't they let you opt out, but they also try to get around your filters.
I agree with this for a large part. (Fortunately, my filter software isn't fooled this easily most of the time.)
It would be great if we could come up with a way to make sure the subject better reflects the content of a message, both to avoid this type of spamming and also for regular email, especially in cases where a mailinglist discussion strays but the subject remains the same.
An obvious first step here would be to require that the words in the subject line are also present in the body of the message.