This plugin is great, but could use a few things to top it off.
My biggest complaint is the user Avatar gets removed from the toolbar and I haven't found a way to get it back without hardcoding.
If you just want to edit the wordpress nav menu use "Admin Menu Editor" because it has by far the most options for the left nav menu.
If you want to edit just the toolbar use wordpress symposium because it gives many more options for the toolbar (theming, roles, avatar display).
However, the developer is constantly updating though, so I'm guessing it's not long until this plugin eliminates the need for any other "admin tweaking" plugins.