Well written and I learned a few new things about limitations of the AppEngine platform. Definitely worth reading if you consider trying something on AppEngine so you can know ahead of time what some of the less documented limitations are.
Some of the things the article mentions that I never realized: 1MB limit on python variables, 1000 limit on offset (which together with the 1000 limit on results means you can only ever fetch 2000 items).
Some of the things the article mentions that I never realized: 1MB limit on python variables, 1000 limit on offset (which together with the 1000 limit on results means you can only ever fetch 2000 items).