Would it be efficient to use PHP to load a complete site out of a mysql databases?

e.g.: Customer A requests foo.com, PHP loads the request page from mysql, loads page.

You probably don't want to store the actual code in the database, but you could use it to determine which files are loaded into each page.

This site (and all other vBulletin sites) pull thier entire html and templates from mySql database tables. This benifit allows the templates to be edited through an admin panel and also allows for another layer of PHP parsing before the output is sent out the buffer.

^ You could just as easily use static files with an admin panel, which would probably be more efficient.