In addition to weak keys, I would not be surprised if most of the time they actually just steal the keys off the subject's system (and install keyloggers for ca

In addition to weak keys, I would not be surprised if most of the time they actually just steal the keys off the subject's system (and install keyloggers for catching the passphrase). The "Bundestrojaner" (federal trojan) has been widely reported and even if the police no longer use that particular software, I'm sure the secret service have their own, similar tools. The other thing is that often, knowing who the subject is talking to and when is probably half the battle. PGP doesn't intrinsically protect against that.