Can't undo upvote on comments. The comments area understandably has a small interface and I accidentally upvoted the wrong comment. Apparently they cannot be un-upvoted.
Oh, no! Now you'll have to forever bear the shame of having anonymously upvoted a comment, which has little to no impact on anything whatsoever!
Seriously, though, I agree with you. It's not high on my list of complaints (why am I still unable to remove a vote to close), but it's on there somewhere.
On a similar note, I wish there was a way to downvote a comment.
If a commenter puts "the best way to access elements in the HTML page is to use document.all" I can't downvote this. I can post a comment pointing out why it is wrong... and hope for upvotes... but the comments were never designed to support a hierarchy... thus later when someone sees the "minified" comments (based on votes) all they see is a rant that has nothing to do with the original question / answer. :-(