Kind of silly that you wouldn't use MongoDB yet you'd use GAE. GAE is a turd, Google has been struggling to compete in the cloud business and failed to come out with any value. You get locked into a Heroku-like platform with awful performance, awful stability, and arcane quotas.
Thanks for the feedback. I would encourage you to note that those blog posts are from 2010 and 2009, and my understanding is the platform has improved dramatically in the ensuing 4-5 years. I'm a Linux systems engineer, but for an app where I'm not going to admin my own infrastructure, I have been happier with App Engine than other PaaS options.