There are two files in ~/.osso/hildon-input-method/ that should be of interest:

.personal.dictionary
.used.dictionary

The first time you enter a word not already in the dictionary (including mispellings) it goes into .personal.dictionary the second time you use the word or select it in the auto-correct it goes into .used.dictionary and is removed from .personal.dictionary

If you only mispelled or used words once, you can delete the .personal.dictionary (I haven't tried editing it)

The system recreates those two files (.personal.dictionary and .used.dictionary) if they don't already exist, so they can both be safely deleted if you want to clear out the auto-correct completly.

- mars