Can a Drupal site design (not just colors, fonts, etc -- template stuff) be replicated over multiple drupal sites?
Just to be able to replicate additional fields that you may add to bundles on a "master" site to several other sites, you may use Bundle Copy.

This project provides export/import support for:


Node types
Taxonomy
User
Field API fields
Field groups


It will only export/import the bundle definition, not the content.

For a more elaborate export/import module that not only handles fields, but whole features, take a look at Features.

From the module's description:


  Features provides a UI and API for taking different site building components from modules with exportables and bundling them together in a single feature module. A feature module is like any other Drupal module except that it declares its components (e.g. views, contexts, CCK fields, etc.) in its .info file so that it can be checked, updated, or reverted programmatically.