Is Google App Engine a worthy platform for a Lifestreaming app?
If you're app solely relies on Django, then App Engine is a good bet.  However, if you ever need to add C-enhanced libraries, you're up a creek.  App Engine doesn't support things like PIL or ReportLab, which use C to speed up processing times.  I'm only mentioning this because you may want to use C to speed up some of your routines in the long run.
If you decide to use a co-loc, check out WebFaction.com.  They have great Django/Python support and they have no issue with you using the aforementioned lirbaries.
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?