I have been investigating the Facebook Open Graph API. There is a \"manage pages\" extended permission which allows publishing to a user\'s Facebook Page news feed/wall via \"im
It is worth noting now, for anyone viewing this question (which is celebrating it's 1st birthday!), that Facebook significantly upgraded their API functionality back in July 2011. You can now Add, Remove, Rename, Reorder and set tabs as Default via the Open Graph API. The blog post is here:
https://developers.facebook.com/blog/post/524/
And the official documentation is here:
https://developers.facebook.com/docs/reference/api/page/#tabs
What Facebook does NOT have yet is a new API method for creating new tab apps, or for changing the tab icon. This is a big step though!
UPDATE: There is bug on the new bug tracker to follow about creating apps in the API if you want to follow it and see what they do: http://developers.facebook.com/bugs/295627350461318