People who use one of those sender verification services to stop spam annoy me. It annoys me even more when I get messages from them because some spammer has forged their from address. I've been blacklisting people with SpamAssassin:
One thing that I found helpful is to make the score for being in my blacklist double the default, so that if they are also whitelisted it doesn't cancel out. Somebody thinks they are clever by spamming me with a faked email@example.com address.
score USER_IN_BLACKLIST 200.00
I've got a server at home that I run apache on for testing. Problem is that my ISP helpfully blocks port 80. I set up iptables so that port 8080 works the same as port 80 so I can access it on a sensible port at home.
iptables -t nat -A PREROUTING -p tcp --dport 8080 -j REDIRECT --to-ports 80
I like it how my ISP uses their firewall to make life harder for me rather than using it to help me. They don't seem to block any sensible ports, perhaps if ISPs blocked 135 we wouldn't have so many problems with worms.