Now, I've added the native spell checker interface for mac os x, I find it strange to support only adding words in LyX. It seems like the spell checker infrastructure doesn't support removing of words from personal dictionary. But this is possible with aspell at least, AFAICS.
The cool feature here would be to dynamically add the "Forget word" item to the context menu if the selected word is in the personal dictionary. (And make it work of course :-)) I don't know how difficult this is to achieve - but I'd like to investigate here. Any opinions or comments or hints? Stephan