A lot of the suggestions here would require changes to the server software, but I have one that might be fixable by only HTML and CSS changes (e.g. by switching to a good old HTML TEXTAREA element).

Less Wrong has a bug that makes it almost impossible for someone in the habit of reading Less Wrong with large type to compose a comment without temporarily decreasing text size. The bug has definitely decreased the rate of my contributions. Specifically, at the larger text sizes, the rightmost part of the box into which the person types "goes under" and is consequently obscured by the sidebar. This screenshot shows the box going all the way under the sidebar and peeking out the other side. Although the screenshot shows Firefox, the problem occurs in Safari, too, and (for reasons unrelated to Less Wrong) Chrome is not a reasonable choice for a person who prefers or requires large type.