I got a chance to try it out just to see if a simple URL fetch was blocked:

http://helloworld-111.appspot.com/

Locally, this code reports 200 OK for all of those except the last reports a 302 redirect (to the https, I presume). As you can see, on Google, they all fail with an internal exception.

Paypal does have a universal Disallow in robots.txt, so I thought I'd setup why.gd to do the same. But it works fine.

Anyone else find any other URLs that are blocked?