I just got an email that HTTPS is available on Google App Engine now. This is absolutely huge for people that wanted to build commercial applications, or talk to third party APIs, such as Amazon S3. Great job Google!
Jonathan Saggau, and I are presenting at the O'Reilly iPhone Live Conference, and we needed HTTPS, so this will make our talk even better. We are going to demo a commercial app that will be released that same day, and it does in fact use Google App Engine, and Amazon S3.