The quick-submit of comments through the Enter key is a real nuisance on this site. When inputting Japanese through an IME you are required to use Enter, which also submits the comment. Having to remember to hold Shift every time is annoying and may even interfere with some IME's input (possibly, I don't know).
I use this user script. This at least prevents the Enter key from erroneously sending a comment when you are writing a new comment. This is just a workaround and not a proper fix, but an incomplete workaround is better than no workaround.
Edit: The old version did not prevent the Enter key from sending a comment while editing a comment, but the new version (June 7, 2011) does.