Is Google App Engine a worthy platform for a Lifestreaming app?
It might change when they offer paid plans, but as it stands, App Engine is not good for CPU intensive apps.  It is designed to scale to handle a large number of requests, not necessarily a large amount of calculation per request.  I am running into this issue with fairly minor calculations, and I fear I may have to start looking elsewhere as my data set grows.
I'm building a Lifestreaming app that will involve pulling down lots of feeds for lots of users, and performing data-mining, and machine learning algorithms on the results. GAE's load balanced and scalable hosting sounds like a good fit for a system that could eventually be moving around a LOT of data, but it's lack of cron jobs is a nuisance. Would I be better off using Django on a co-loc and dealing with my own DB scaling?