It's important to understand what these guys are doing - they analyze
your spam and report it to law enforcement agencies, anti-spam groups
and others places (like the spam site ISP and hosting provider).
On top of that, their Blue Frog software automatically visits the sites
advertised in the spam messages you receive and posts a complaint
demanding the spammer to stop spamming the communtiy.
The system is very well thought of (easy and safe to use) and results
are encouraging - I now receive less than half of the spam I used to
get 3 months ago.
see
http://members.bluesecurity.com for statistics.