Copyrighting a Dynamic & Everchanging Website?

If I understand correctly when you create a finished work, you can register for copyright and submit the work to the copyright office. But what do the big websites that are constantly changing every day do to copyright their work? I read a cached version of copyright office circular 66 (as the real one is currently under review) and basically what I gathered was every time I make major additions to my websites, then I should send in a new copyright for $30 and I can register database updates separately, every 3 months.

Does anybody here have a rather large website they maintain that they register copyrights for on a quarterly or yearly basis? I'm wondering exactly in what specific form everybody else submits their dynamic websites & databases to the copyright office in and how often?

I was reading joebert/Dr. House's post on sending a DMCA Takedown Notice and it got me thinking about my own copyrights.