I try to use the same (or similar) templates and software across multiple web sites.
Right now I am running Wordpress, Drupal, Joomla, and vBulletin. Obviously my execution isn't following my strategy.
I am going to make an attempt to switch from Wordpress to Wordpress MU, to make updating easier.
Likewise, I could run all of my Drupal sites from one instance of Drupal. That would also make updating easier, and Drupal can be annoying laborious to upgrade.
Joomla and vBulletin have no similar functionality, so I'm out of luck with those.
I built one web page which is nothing but a list of all of my web sites, grouped into categories. I use it as part of my "Control Panel" for managing my "web empire."