Malte,
The on-hover help is an interesting addition. Please don't make that a default or remove the option to have the help text displayed inline. For some reason I think it is easier to just show the help then make the user play a little game by pointing at the question mark and hoping something interesting will happen.
So as an option I think its a great idea.
On spellchecking, again not everyone would choose to use spellchecking, but it would be great if when HTMLarea is used the HTMLarea spellchecker in enabled, and if it is not used the OpenACS spellchecker is available.
