Like DougMcLean, same thing happened to me. With every other version of iOS in my AppleTV 2, I had YouTube, Radio etc items in the menu. Now after updating to the latest version everything is gone except for Computers and Settings. FYI, I am in Malaysia where the AppleTV is not sold. I got mine in Oz.
I tried Settings to see if this is simply a setup issue, but there is nothing that I can see that relates to this problem.
I have not tried studiogalatea's solution. By pulling the plug, do you mean that I simply remove power?
Still I wonder what Apple is doing? Even if I am not able to buy movies in Malaysia (I guess its because of IP rights and piracy) I don't see why Apple has to cripple the device and only allow me to share my computer's content and nothing else! This is quite ridiculous. I can view anything on YouTube, Internet Radio etc on my computer anyway, since these sites do not prevent anyone in the world from viewing. So has Apple become everyone's conscience?