Alright, this node is begging for some hard factual and conceptual information so here goes.
Late update: all posts on this topic other than my writeup were klaproth'd. Admins felt this was the only writeup with a point. Please imagine that someone made a silly statement that 'real hackers' avoid FBI detection by creating private networks over IRC, everything will make a lot more sense. Thank you.
Having a 'private IRC network' isnt really an elite thing to do. It's really easy, you download a server, set it up, run it. Cackle maniacally for a while with your irrevocable super admin privileges and then wonder what the point of it all was. As previously stated, any unencrypted (and yup, IRC is unencrypted) traffic over the internet can be sniffed and logged. It is also highly likely that you ARE being logged, because 'private networks' for 'l33t hax0rz' attract feds like wasps round a garbage can. If you don't believe that, #hacked on DALnet had a fed lurker who we couldn't keep out, because he seemed to have an unlimited number of domain names he could come in from. The only way we knew it was the same person was by probing his IP address.
IMHO, real hackers use not private networks but public ones. Public networks such as AOL Instant Messenger and e-mail are easy to secure - PGP encryption makes it all easy. Not even the NSA can crack a PGP message before its contents become obsolete, and unless you're a mafia boss they aren't going to expend the energy. It's much easier just waiting for you to actually attempt something illegal and then catch you that way. The strength of a public network is that it is unlikely that you will be singled out. Unless the authorities know to look out for you, you will blend in with the terabytes transferred every day legitimately.
Private networks on the other hand, can be an extremely effective way of advertising that you have something to hide. Using a 4096-bit PGP key is a little suspicious. Having an open port on your machine that regularly passes a great deal of 256-bit AES-encrypted traffic is a LOT suspicious. Building your own encrypted networks over the internet is a very simple affair if you're a good enough coder or know a good enough coder. Keeping their existence hidden is another affair. Encrypted traffic passing through a government sniffer (such as Carnivore) is highly conspicuous, which will lead to a permanent tap being placed on your connections.
If you must use IRC as a means to co-ordinate or brag about hacks, I would suggest the use of Invisible IRC. It is a newly developed, peer-to-peer and fully encrypted IRC network. Perfectly unreadable, and mostly untraceable without great effort. Run a google search for it, and may you live longer outdoors than in.