There have always been #perl channels on the big IRC networks (such as EFnet), but a couple of years ago a smaller, Perl-orientated IRC network came about: irc.rhizomatic.net. #perl on there was full of friendly Perl people who used Perl to get things done. A friendly place, not full of clueless newbies as the rest of the Internet seemed to be. The rhizomatic community started off small, and increased every Perl conference as the word got around and people met In Real Life.
Back to London: The London.pm mailing list got quite silly about a year ago. It wasn't uncommon to receive hundreds of posts a day. I even started doing a weekly summary. The reason is that the list was extremely social, which was great, but scary. Over the past couple of months (and especially after yapc::Europe in Amsterdam) a lot of witty one-liners that would previously had been posted to the list, made it to the #london.pm channel on rhizomatic. Socially, it's great, as it's all real-time and there are people with lots of experience there.
As I type, there are currently 40 people on #london.pm, which is the biggest channel after #perl. Of course, some of them aren't actually in London (the London.pm family spans across the world), or even alive (there are a couple of bots), but it's great being able to talk to everyone there.
Recently, some other projects have started up channels on rhizomatic, which brings lots of friendly, intelligent people to chat to. POE was the first (in #poe), and now the XML-mad (in a good way!) AxKit people (in #axkit) and most of the Parrot people (in #parrot) have joined in too. This makes it a great concentration of the best Perl minds and I've learned a lot by lurking there.
Some employers look down on IRCing during work time. Sure, it's possible to spend all day chatting, but simply being around helps you to learn new skills and tricks. Try it and see.
I own the first European irc node (london.rhizomatic.net) and it has been great to see the users and channels grow.
Thanks to all the rhizomatic crew and YAS for starting it all! And see you all online...