Nothing prevents posting forms on facebook that call up a PHP application that sends the user request to the site owner. These forms are a good way to get leads.
By using iframes on Facebook one can assemble information from multiple sources to present useful content to visitors. Such as in this case Border Wait Times
To use (animate) HTML5 canvas images on facebook the images need to be converted to base64 – Base 64 encoder and use a data uri for the image – because the Canvas requires the image come from the same domain as the html5 script and when using facebook with iframes the domain for the image on facebook would not be the same domain as the iframe or fbml domain … CDN are in use with facebook images.
Update: Progressive Content – Ajax on facebook …
One of the differences between the old and the new facebook API is Iframes. By using Iframes content can be used from any host where one can place a 520 x 800 (or with 8 pixel margin 504 x 784) document. The limitations of content is limited only by facebook policy. If there is something in the older API that can not be done with the newer API I am at a lose to identify it — other than the difference it makes for SEO.