Peer Guardian 2 has long since screwed up on my machines. Years ago it worked perfectly, but at some point various problems appeared like blocking 0 IP addresses for no reason (presumably mass corruption while downloading of all lists it was supposed to manage), random GPFs and then in recent years not spawning a window or systray icon (literally a windowless-process) meaning I have no idea if it is working or not.
I tried the RCs etc, but still the instability and bugs made it unviable. I was planning to look into uTorrent’s built-in functionality to filter based on IP addresses as a second-best alternative, but haven’t got round to it yet.
Thankfully, some kind people have forked Peer Guardian 2, creating PeerBlock! (found via the Phoenix Labs RSS feed). So far this has successfully installed on all of my machines, and I hope it will continue behave itself and be worthy of standard install status like Peer Guardian 2 used to be.