I then realised that if large numbers of users began to use your script, then Jay's server would be under extremely high load just around the hour of each day, and especially during specific US times.
He then went on to suggest a tiny bit of code for how to workaround this problem - it works by generating a random interval of time for the script to sleep before accessing the MT-Blacklist master blacklist changes RSS feed. Er, yes I didn't think of this at all and all credit to Edward for pointing this out.
Go get it if you're interested - to upgrade from 0.1, just simply replace the existing files with the current ones. Of course, you have to change the configuration settings in updateblacklist.php again, so make sure you copy them out from the old file.
Also, I haven't upgraded MT-Blacklist since version 1.62 so it would be nice to know someone could tell me if MT-Blacklist Updater breaks in the newer versions.