Just saw http://stackoverflow.com/tags/php/topusers and seeing 18% unanswered of ~400k seemed like a lot. I'm guessing there's a tag with more unanswered answers, right?
Which is the tag with the most unanswered questions (not percentage)?
Bill presented a query for this, and results as of the end of 2012 in his question "Help us clean up the Android tag." The query you want can be found here, which I believe is the original creation of Jon Seigel and Greg Hewgill.