to add more, sometimes, even if they use a dynamic address connection, DNS black lists may catch them on one address and block it for 24 hrs.
Spammers simply reconnect, get a fresh address and start all over again.
Obviosly, as retsila mentioned, using your own DSL connection, on the long run will lead them to you.
Not all countries, though, consider this an offense: if you look at ther hundreds of spamcop listing in your morning logwatch email, they usually come from countries where breaking people's balls with spam is not yet considered an offense.
I am not mentioning any of these countries but you can find out by doing a simple traceroute on the address in the spamcop report.
QatQat
If I could have sex each time I reboot my server, I would definitely prefer Windoz over Linux!