We typically leave Seven as the admin theme on Drupal 7 sites, and use Rootcandy as the admin theme on Drupal 6 sites. One of our large clients installs Rubik whenever we deliver them a site.
A good admin theme can help, but it is really just lipstick on the pig.
I will also agree, to an extent, that Workbench can be of use for content creators on sites that are adding lots of new content.
However, the administration problem for Drupal is solved by doing three things:
Only install the modules that you actually need. Once you have a site ready for deployment, disable and potentially uninstall anything that you don't actively need. This reduces the number of entries in the admin menu.
Set up a proper set of roles and configure the bare minimum permissions that each role needs. Even if a single person is running the site, set up a non-administration role for their user that they will need for daily tasks. Save the uid 1 account for occasional tasks. Again, this reduces the number of entries in the admin menu.
Set up as much contextual help as is feasible and train the client. It is especially helpful if you can match up features in your site to a good book, like The Definitive Guide to Drupal 7.