When I disapprove an article I usually leave a comment for the author anyways. Most often it is because:
The article is poo.
The article is a tip.
The article is great, but looks like poo.
The article is great, but the spelling and grammar are poo.
I recently offended an author because I said I wouldn't approve it if it was written in all lower-case. I don't know if others approved it or not, but I felt it reflected poorly on CP.
Often I find good articles from people who do not speak English as a first language and the article has enough errors to reflect poorly on CP. I always thank them for their submission, tell them why I think it is great, and ask that they please ask for the help of an editor.
I do not want to invite flames by PM, but if it can improve the general quality of articles, I'm fine with my vote being shown.
On a side note, giving us the simple ability to convert and Article to a Tip would go a long way.
I voted no. If a dismayed author asks for clarification on a "disapprove" vote (I doubt they would care about an "approve" vote), I would most likely provide a reason, thus revealing the fact that I may have in fact been one of the "no" voters. I don't feel that it's necessary in every case, though, and I definitely feel better about it being my choice when to publish such an opinion. I don't think I'm alone in this. My guess is that, if all votes became public knowledge, fewer people would vote on the moderation queue, which would lead to lower overall quality for the site.
In my opinion, all "votes" should be public. Even a vote of 5 in an article.
This will probably reduce (at least a little) those many votes given by friends to bad articles.
But looking at it differently, I believe that today users expect smaller articles with some block of code they can simply cut and paste instead of large articles with deep explanations. Maybe the quality of readers has already lowered a little.