The company I'm currently working for is called Digital People, a creative agency based in London. We make exclusively Drupal-based sites, which normally showcase the results of market research, and increasingly act as portals into the research departments of large companies.

We develop using a subversion based workflow. Here's a great article by Nick Sergeant which closely approximates our current development practices:

http://nicksergeant.com/blog/drupal/my-thoughts-small-scale-drupal-development-production-environments-cvs-and-subversion

The only difference being that we don't check our "files" directory into subversion, as it often contains video and other large files.