The client approached us to assist with automating the running of 40+ sites.
The first site was running on a WooThemes theme, so our first suggestion was to make a reusable child theme. After setting that up, we soon discovered that the theme was too resource intensive (for the purposes of this client) and offered much more than the client would ever use.
We then went ahead with building a master child theme based on TwentyEleven instead, with built in adsense metaboxes. We also developed an alternative for the very resource intensive YARP (yet another related posts) plugin and we set up the SEO.
After we implemented the child theme on the first site, everything worked fantastic and the client wanted us to roll it out over the 40+ other domains.
We advised the client to use ManageWP to manage all these sites simultaneously. We went ahead to prepare all domains for a brand new manual WordPress install with complete database setup with the master child theme.
In the end the client only needed to spent a few minutes per site to be able to make the settings site-specific.