It would be awesome if the textarea elements one uses to create/edit comments on M.SE were larger and allowed for more characters. The ones on MO are perfect, for example.
(Why do I want this? Well, I just wrote/edited a longish comment and doing it without a preview in 3 lines is a bit annoying Also, I had things like T(\mathcal U(\mathfrak g)), which get counted by-the-character!)