invite people to add application

There's nothing stopping you from creating a page with fbml markup like the other apps use. Then direct your users to that page.

At the moment, Drupal for Facebook has no features specifically to make this easy. I encourage you to develop an add-on module that does this, and submit it here in the form of a patch.

This request supports the need to address intelligent management of FB-specific modules / callbacks per here -
http://drupal.org/node/188106

We need a framework to address more than just invite control - but any FB-specific logic.

I think an fb_invite module would be a useful addition. It could render a form and perhaps direct users to that page on their first visit to the app. However, we can't assume that all apps will do this the same way. Some may not want it at all.

Regarding the hooks, there is already hook_fb(). It will notify any module that a canvas page is being served. There is also hook_user(), which notifies any application of new users. An intelligent module could work with those. Maybe it makes sense to call hook_fb again with an op of FB_OP_NEW_USER or some such, when fb_user.module creates a new account, if that makes it easier. But a module that relies on hook_user alone is more likely to function properly in the context of Facebook, Open Social, and other modules that create new users. That is, why make a module facebook-specific unless it really needs to be?

I'm open to patches.

Since Drupal 5 is no longer supported, I'm taking the liberty to close all FB D5 issues. Issues that haven't moved since D5 are unlikely to still be valid.