I've used some that deliver "traffic" for as low as $.005 per "click". It isn't robot traffic but its not exactly a click either. It's a pop-up or under. Whereas the signup rate for the site from G traffic is typically between 1 in 20 to 1 in 35, this type of "traffic" was about 1 in 150 and some people from it did end up becoming paying members.
Found them through AdWords though, not email spam.
We have a script that we have written that tests domains, all it does it pings a domain, refreshes the IP address and pings again. I am sure they use scripts such as these to deliver this "traffic". The best use of these programs is to artificially inflate numbers to show a potential buyer of the site.