Yes. Absolutely. In fact, one of the options for developing a Facebook application is a built-in frame that points to your site, which can be anything you want, including direct HTML web service.
There are two officially authorized libraries for accessing information on Facebook, and one of them is based on Javascript.
You can do quite a bit on Facebook using Javascript / HTML. There are many opportunities to use the services outside of your own site (think Flckr, Google Ajax API, etc.)
Facebook applications are pleasantly easy to develop.
The documentation is indeed located at: http://developers.facebook.com/
I would also like to note that traffic from the point of view of Facebook, everything can develop rapidly. There are student stories of creating apps that scale quickly for millions of users . I am not saying that this can happen to you, but it can be an effective and highly viral distribution platform.
cgp
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