Overall, 2.1 is a winner! Big kudos to the entire WP team.
That said, here's an annoyance: In 2.0.6, the rich editor allowed Firefox's built-in spellcheck to operate. I liked this, as it did not require the hitting of a button, as I am now forced to do in WP2.1.
So, in short, I want my post textarea to play nice with Firefox 2's built-in spellcheck again.
EDIT: sorry for placing this in "Install." I didn't see the categories until after I submitted.