How can I make a View that shows the number of nodes attached to per taxonomy term?
This may help get you started. What you want to do can be accomplished by creating a views entity with a taxonomy argument that returns 'display summary when argument not found.'  In that setting as well is an option to display the number of nodes, (339) for example, that have that term attached to them.

http://drupal.org/node/301485#comment-1065230

Check out that link and post back with questions.