Update: Looks like I was a little slow off the mark to fglock here :)

You have a problem with the precedence of the trinary operator as compared to the = I believe.

Adding brackets will help you no end :) Like this...

 for (values(%{$hash})) {
   /yes/i ? ($_ = 'Yes') : ($_ = 'No');
 }
[download]

HTH,
Neil