Apparently, users are going to the website, clicking login, and are confused when it doesn't provide access to the service. They're not reading a word of the documentation -- they're just seeing a login button in the top right corner and clicking on it.
That prompted us to put a banner at the top of the page:
Attention New Users!
This site is the documentation for the service. It is not the actual service. The login link in the upper right corner won't log you into the service.
To use the service, follow the instructions linked from this page.
We considered s/New Users!/Dumbass/, but figured that wasn't very polite.