The real problem was for potential SORBS users – if they followed the instructions verbatim, they ended up rejecting 100% of your inbound mail. Sadly, I've seen traffic, which implies that this has happened to some degree.
If you're going to use the SORBS blacklist, be very careful to make sure you've implemented it correctly. Both this, and SORBS' claim that dnsbl.sorbs.net is an unsafe zone to use, suggest that the SORBS' list may not be a wise starting point for those looking to simply, safely block spam.
More information on SORBS can be found here.
There has never been a blacklist with a zone name of dnsbl.radparker.com -- and if you type that into the DNSBL section of your mail server config, you will break your inability to receive inbound mail.