"Has anyone here seen evidence of IRC-borne paedophilia?"
Sort of. A channel I used to op in often got 'perverts', but most of the offenders did all the offending in PM, therefore, I would load a clone and say something like "12/f/florida, asl?" on the main - I often found people telling me they were 23 (or older) and, thinking I was 12, asked me all kinds of sexual questions, sent me dirty pictures etc. - obviously then promptly perm banned.
"How is one to determine that a user is committing a crime or about to commit a crime and not necessarily just talking dirty?"
Crime is such a yucky topic, due to all the different laws, particularly in this area of the law. I would assume 'one' is not to assume anything, but rather, leave it to appropriate law enforcement agencies to do something about it? These people are not caught because someone on IRC tips them off with some Query logs, it's all credit card records, intelligence, etc.
It's a disgusting thing, and it's something which everyone knows can (and does) occur in online chat rooms, IRC being no exception - hence the constant "don't give out your real name, address, phone number" advice splashed everywhere. It was, supposedly, one of the reasons MSN closed their chat rooms to the majority of the world too.
I know some people believe anyone under the age of 13/14 (or older perhaps) should be supervised by their parents when online. This is, in practice, a fairly ridiculous and impractical notion for the average mother/father, and even less applicable to a user of IRC who may be on IRC for 4-5+ hours at a time. It's more sensible, IMO, to educate people as to the dangers. However, realistically, this still won't work too well - "Smoking kills" and "Smoking causes a slow and painful death" is plastered over cigarette packets, it doesn't stop people smoking. Speed cameras don't stop people speeding. In the same way, a 13 year old isn't going to stop talking to their 33 year old friend on IRC because they might be a paedo, because the age barrier is not as big an issue - there are plenty of really really nice 30+ year olds out there who I talk to online all the time (myself being 16), none are paedophiles though.
Privacy is an important thing to retain, but those that really want privacy so badly they want to make a big song and dance over it, I would assume, have something to hide? If police suspected I had child pornography on my computer and wished to search my computer, I wouldn't even ask if they have a warrant. I've got nothing to hide. Agencies (i.e. FBI, Police, etc.) should always have to inform you their searching your computer, no underhanded crap, but I don't see the issue really.
So, as I see it, it's not as bad as the media would like to make out (as far as online chat rooms are concerned, which they constantly seem to mention), but the problem is never going to go away, with or without the Internet or IRC.
My 2 cents.
Regards,
