I spent a good 30 minutes trying to figure out how to give a User administrator access throughout all of the the WordPress MU blogs. Here’s what I found:
1) Under the Users Menu, click on the User’s name
2) Click on the ‘Grant this user super admin privileges for the Network.’ Radio button.
3) Scroll down and click ‘Update User’
That’s it! You’re finished.
Now that user can do things like installing plugins or themes sitewide. Slick, isn’t it?