I did some spreadsheet-ing to look at the "profitability" of their userbase. If the business were sustainable, then Monthly Recurring Revenue [1] would be higher than the cost to service the customers [2]. If not, then growing the userbase just increases total monthly losses (assuming a steady freemium conversion rate).
In Everpix's case, it appears they were growing unsustainably.
Their data shows that all the way up until February 2013, they were spending $3 on AWS for every $1 of MRR. That's scary, because it means that a new customer bringing $1 MRR was actually increasing their monthly losses due to usage costs!
Things got better though. In March and April 2013, a surge in premium users seems to have shifted the balance in the right direction. But still, for May 2013 until the shutdown they were spending $1.20-1.40 on AWS to service every $1 MRR.
So growth in their userbase was actually increasing their total burn rate, which makes growth unsustainable.
You can see the spreadsheet analysis here:
https://docs.google.com/spreadsheet/ccc?key=0Ap7fmpANG_0QdHV...
[1] https://github.com/everpix/Everpix-Intelligence/blob/master/...
[2] https://github.com/everpix/Everpix-Intelligence/blob/master/...