Colloquy spits out lovely XML transcript files when you export them. In the absense of finding an easier way to convert them, here's a simple script to convert them to plain text.
bundle install
./convert <path-to-transcript> > output.txt
- The timestamp is outputted without the date for brevity. You might want to edit this if you have logs spanning multiple days.
Do what you like with it :-) but I accept no responsibility.