Would be nice if Gmail's "Spam" button actually blocked future emails from that same person indefinitely!

Sometimes they get around filters by sending from different emails, that's really annoying. I should probably quit Gmail and go back to Cerberus which has awesome filtering!

I too was looking for that button, and the best that I could find was drumroll to create a LinkedIn account and change my preferences. :/

For the end user that isn't a member, they seem to not want to let you opt out of their emails.

That wouldn't prevent them to build a social network around you, just like Facebook does ("ghost profiles" or whatever they are called these days). Those emails are just spam.