[button] 1. My first idea was that this has something to with line breaks but it is for adding non-breaking spaces ( ) like you said Alan. This is a totally useless button because you can as well type several spaces after each other in tinymce and tinymce changes them automatically to non-breaking spaces.
I have to disagree. The non-breaking space is absolutely indispensable for French-speaking users, as it is needed before so-called double punctuation marks (: ; ! ?). It is true that if you type more than one space in tinymce they are automatically changed to non-breaking spaces, but we do not want 2 non-breaking spaces before double punctuation marks in French, we want one, and that button is therefore indispensable to us. This is one of the most needed improvements in tinymce over current moodle HMTL editor that we need for French (and maybe other languages as well).
buttons 2 : might be useful in some circumstances
button 3 : very interesting; quite useful as you say to mess things up
button 4 : would be more useful if it also displayed the end of paragraph ¶ sign (as in Word processors)
button 5 : I agree that it duplicates the Find button to its left. There is a bug, replacement does not respect actual font but default font.