What's great also about Facebook is that it carries EVERYTHING after your ../appname/{things-beyond-your-app-name}
to you hosted [server] URL... so that even .htaccess can be used. ;)
Like this...
http://apps.facebook.com/YOURAPPNAME/a/b/c.htm
For an app that's hosted on my server at:
http://example.com/APPSHOSTEDPATH/
and by using this one-liner included in my hosted location's .htaccess file in:
http://example.com/APPSHOSTEDPATH/
where .htaccess file contains (among the other standard) lines...
I can put something like:
RewriteRule ^(.*)$ /myRedirectedPath/$1 [L,R=301]
So if the person goes to:
http://apps.facebook.com/YOURAPPNAME/a/b/c.htm (as in the above example)
They'll stay there and they'll be accessing:
http://example.com/myRedirectedPath/a/b/c.htm
(pretty sweet, eh?) ;)
Fun stuff... wanted you to know that there's more capability that just $_GET
's.