A hint to all companies offering access to their platforms via an API: look at your API documentation sites as an opportunity to build a community around your API. Do not require users of the documentation to login to your service to read the documentation, do not require them to click through arcane paths to "find" documentation. Make it as easy to find the API documentation as it would be to find your blog or support site (i.e. http://api.yourcompany.com).
Why make it hard for folks to evaluate your product for the purpose of investing their time and effort into building your community of users?
I'm proud to say that not only does Socialtext make their API documentation public, its on a wiki that allows for feedback inline. In fact, Facebook and Twitter (and many others) use wikis for API documentation - a practice I highly recommend. What better way to create dialogue and community with your developer/users than giving them a direct means to give feedback on the APIs they are being asked to use?
