Thanks. Shame about the stage.maemo.org certificate expiry (please vote for bug 5551). I couldn't find anything immediately helpful there. It looks like the word completion stuff might be in a separate module, which may or may not be open source. Anyone know?
A bit of searching makes me believe the word completion stuff is in hildon-input-method-widgets, which I believe is closed source unless anyone knows differently, which is a shame.
I had various smutty words in my prediction file, which could be embarassing for me. I found the file using "strings" etc, if you just delete it it gets created afresh next time you type an unusual word which is good.
so yeah to get rid of all the pr0ntastic / personal words in your user dictionary file, use th Xterm and copy-paste this: