A spell checker would be a bonus, but not a necessity. My biggest concern is that such a feature may slow the site and rating process down. Presently, I will often test a comment in a word processor to check for spelling before I submit, and I assume that most everyone can do the same if motivated. Thankfully, RateItAll eventually fixed the bug that cleared the helpful/not helpful clicks when one revised a comment. This allows one to subsequently clean up the spelling without losing the feedback history.
