Cropping, scaling, and resizing images on the fly, for free, with GAE. Great service, wish AWS had something similar

App Engine API has a very useful function to extract a magic URL for serving the images when uploaded into the Cloud Storage. get_serving_url() returns a URL that serves the image in a format that allows dynamic resizing and cropping, so you don’t need to store different image sizes on the server. Images are served with low latency from a highly optimized, cookieless infrastructure.

or, really, 'why we had some glitches and outages recently'. A few interesting tidbits about GAE innards though (via Bill De hOra)