According to a report from Microsoft and Google spammers world wide rake in around $200 million in profits, however while doing this they are also costing the receivers of that spam around $20 billion. Unfortunately given that the $20 billion is paid by all of us and not the people that are making the $200 million I don't see them stopping voluntarily anytime soon.
There are fortunately some encouraging developments that could end spam forever (At least in its current incarnation). For instance DMARC which combines Sender Policy Framework and DomainKeys Identified Mail seems a promising technology. If you want to know more about DMARC there is a whole episode on it with Security Now. One of its most important features is that it is supported by all the big guys like AOL, Gmail, Hotmail, Yahoo Mail and Facebook. That said it is something you need to set up on your own mail domain so it will probably take a long time before this is supported universally. Hopefully we are moving in the right direction though.