I'm guessing the way that could be linked is when you're using clearnet and you can see your IP on irc, could be linked through what's called "coincidental occurrence"
ie. watching what IP is active at certain times when transactions happen, plus if they are a seller they could guesstimate a link between IP and the transaction.
This is just my best guess of the process someone might use.
I thought I read somewhere that's how bitcoin transactions were being traced - coincidental occurrence / pattern analysis.
Okay, I get it. So VPN, Tor or I2P would solve this and obscure the real IP for those that care to hide it. I guess it is inevitable to use this technology for dark markets and people are going to want to hide their IP. I was hoping this would be an eBay buster, not a dark market but I don't see why it can't be used as both if we add filters.
I2P is built into this coin. I need to play around with it. I see code to support Tor but I don't think it is fully implemented except for a masternode setup. Maybe a built in VPN (like VPNcoin) would help?