After installing the plugin (v. 0.7) on my site (running WP 3.1.1), a Debug button appears on the Admin Bar but nothing else happens. The entirety of the button has the following HTML:
<li id="wp-admin-bar-debug-bar" class=" "><a href="">Debug</a></li>
I also noticed that debug-bar.js outputs an error (similar on the latest versions of Chrome and Firefox):
c("#debug-bar-handle").outerHeight is not a function
Hope this helps. I'd love to actually be able to use this plugin!