You could potentially affiliate with social networks in such a way as to leave a clear fingerprint; that is, you could be, both in your 'anonymous' and 'real' life, the only person who connects 20 different social groups together. This could be as simple as quoting song lyrics. If you tried to deliberately avoid this, then you could potentially be identified simply based on that -- "these two people have too similar interests to not know each other" or so.

Your very manner of speaking can reveal a lot about you. I vaguely remember hearing a cold reader say something like, "the first thing I get to know about someone is their hands." Similarly, your word and spelling choices can inform others about your country of origin, and can potentially do much more than that.

Tor could have security issues, especially if you don't keep it up-to-date. Even if it doesn't have security issues, you could accidentally choose an entrance and exit node which are in cahoots and can thereby de-anonymize you. This applies less to hidden services, but still does apply. That is, the government could have compromised the hidden server, and thus might be able to correlate your activity.

Speaking of that, the times of day that you're active can already narrow down what countries you may live in, and may reveal roughly when you go to work and when you come back. So, for example, if you're using IRC over Tor, people could probably get a lot of information about you. Supposing that law enforcement has narrowed your real-life persona as a likely target, for example, they might just see if you join and part only when you're home.

If you were, say, browsing Hacker News or some other site, this could possibly be identified simply by looking at the size of the chunks of incoming traffic. This would be more and more common for larger and larger files -- I would not recommend downloading large videos over Tor, and images could probably offer a similar fingerprint.

You could use an insecure application over Tor -- sending BitTorrent tracker requests over Tor (while downloading in the clear) is one of the most common. So, if you tried to start up your IRC client before the Tor proxy was up, and your client happened to detect that its proxy wasn't working and tried to connect without one, that could compromise your identity pretty fast. For that matter, someone could potentially use an exploit against an out-of-date browser or operating system to turn on your webcam and take some pictures. For that matter, someone could hide a camera right behind you. You might consider only using Tor from within a bedsheet fort if you're suitably paranoid.

More realistically, the fact that you're using a bootable live distro could potentially be used to identify you; there aren't so many people doing that and your Referer string might well be unique. For that matter, the fonts installed on your machine might be probed and unique. It's worth checking this with EFF's Panopticlick. If your use of Tor hidden services reveals "he's a Welsh male Debian and Tor user who likes this obscure band," you might be identifiable solely based on that, and it's hard to be 100% sure that you have masked the fact that you are Welsh or male.