Their practices are nothing short of horrendous.
Recently, they have blocked whole /18 block of addresses because there was a botnet in one of the /24 subnets. I asked them to remove the /18 subnet blocking so that unrelated and innocent customers sending legitimate mail are not affected by this, but no, self-righteous crusaders have to be "firm".
Similar was SPEWS/APEWS that stopped maintaining their lists altogether, resulting in huge amount of false positives.
SORBS.NET is an outright blackmailing racket, asking 50USD per incident for delisting - like you can force largely uninformed and negligent customer base to update their router/PC software regularly and to stick to a sensible user behavior MO.