...and one step back.
The blocking ideas I suggested earlier sounded great at the time, but the "deny from sbl-xbl.spamhaus.org" line really is just a waste of time. If I'd spent more than few seconds working out how DNS Blackhole Lists worked I'd have understood, fortunately I've now got a nice simple Pythonic solution that I'll be publishing shortly.
In the meantime if you've been blocked from reading this site directly, it'll be because you're a spammer (mail, comment or referrer) or just dead unlucky, if it's the latter contact me and we'll see if I can help resolve things.