I found this while googling...
Using Python to detect the most frequent words in a file | Zen and the Art of Programming
Its a python script, and many variants, for collecting commonly used words from a text file. It also has links to perl and command line alternatives.
Either way, what I'm looking for now, and it might be helpful if someone else has theirs and could try one of these scripts, are AIM logs / text message logs. Unfortunately I hard reset my phone all the time, so my treo logs are worthless, but I've got a buddy with about 6 months of iphone logs, and I'm sure I've got my AIM logs somewhere... I think those would be a pretty good starting point to run one of these scripts on.
Anyway, I'll post when I start filtering out muh logs <3