Easy enough to check if a relay is open, telnet to the port and send yourself an email.
It's a bit of a blunt weapon to use, but sometimes it's necessary:
http://news.com.com/...3-235632.html?tag=rn http://www.internetnews.com/...article.php/8_281191 Nothing the black list admin can do really about hacks, aside from informing the admin, but if you've been hacked open mail relays are the least of your problems. You can become the jump point for an attack on another system. Once informed the hacked system's admin is obliged to fix their server.
It's totally true though that to get rid of spam you have to go after the people that seek to profit from it. Either by money or by wackiness. The measures I'm talking about just make sure people at least try keep their seatbelts buckled.