When I downvote a question or answer for its content many times there already is a good comment explaining why the downvote is done.
There is nothing like VB 2010 Ultimate and this is a Q&A site not a tutorial site. What have you already tried?
Because of this I don't feel that I should add yet another comment describing why I downvoted and I proceeded with upvoting the existing comment.
However personally I do think it's fair that the other person should know that I downvoted. Would it be possible to fabricate an optional link between the downvote and the comment support? Maybe something like
The following members support this (Harald Brinkhof,...) next to the comment, telling the downvotee why he was downvoted and the weight this comment obviously carries.
Since the option of anonymous downvoting has to be respected this has to be a choice, but I think it would be nice if I could add some proper downvote explication without needing to clutter the comment section, especially when someone has explained my reason(s) better than I can already.