The information given on the git instrutions page for pushing a tag say:
git checkout 7.x-1.x
git tag 7.x-1.0
git push origin 7.x-1.0
However in the guide: Maintaining a drupal.org project with Git (http://drupal.org/node/711070) the instructions are slightly different:
git checkout 7.x-2.x
git tag 7.x-2.0
git push origin tag 7.x-2.0
Note the inclusion of the 'tag' keyword in the second example.
I believe that the second version is the correct version? If so then the git instructions should be updated to this.