It's a great app and I use it primarily to access IRC networks outside the corporate firewall. Trying to remember where I first heard of it and I believe it was Hacker News (recommended in a comment).

To be honest, though, I would probably stick with irssi or Colloquy if it wasn't for the firewall limitations at work. I think it'll be difficult to compete with the responsiveness of a native client app, but maybe people like me who run into firewall restrictions or people who can't install software on their work computer will be the types of people you could market freemium accounts to; essentially, tech savvy business users. And if its techies you're after, I imagine you will have a tough time making money off of ads; most of us just don't even look at them (however, give a look to how Pandora serves up ads). So freemium may be the way to go here. For paid accounts, you might also consider offering a searchable and downloadable transcript log (IRC clients offer this already, but I'm sure you could differentiate by making these logs more accessible).

I'm curious as to what others think about this.