Changes to callback URLs and more
Here's advance warning about some changes that are on the way. Anyone using Drupal for Facebook will need to manually alter settings when these changes take effect.
What you need to be aware of is that all callback URLs will change. Right now, if your site is, say, www.drupalforfacebook.org, then the callback URL (as specified in the app settings form on apps.facebook.com/developer) is http://www.drupalforfacebook.org/. This will change to http://www.drupalforfacebook.org/fb_cb/NNN/, where NNN is the id used by Drupal to identify the app. I'll document this in the README and elsewhere when the change gets checked in.
This change relies on the custom_url_rewrite feature of drupal. If you're using any other modules that require it (i18n for example), then you'll have a few other manual changes to make in order for them to play nice together. I'd like to thank the authors of i18n for inspiring me to use this little-known (and badly documented) feature, and providing the code that served as my example.
There are several reasons to make this change. First, it's going to help fix some URL problems, if your app has broken links to files. It allows me to get rid of the base_url and base_path hacks in fb.module. And as if that were not reason enough, its going to pave the way for iframe support, which is desireable for a number of reasons.
Stay tuned for a patch on drupal.org when it's ready...