I take it that you're talking about the new Backends:
Backends are special App Engine instances that have no request deadlines, higher memory and CPU limits, and persistent state across requests. They are started automatically by App Engine and can run continously for long periods. Each backend instance has a unique URL to use for requests, and you can load-balance requests across multiple instances.
Backends seem overpriced to me; their default backend is a long-lasting process running at 1.2Ghz allowed to use 256MB of RAM and it's priced $0.16/hour ($115/month).
They can shutdown/restart/relocate your backend whenever they want so what they suggest to keep your service live is "Configuring more backend instances than are normally required to handle your traffic patterns" (yeah that's at least another $115/month fee).
At linode that kind of money will give you 4G of ram, cpu power in the same ball park and loads of storage and transfer.
It seems that Backends - and the GAE in general - makes most sense when you view the system as a whole, and work with systems of a certain size. Tasks goes in to queues and backends are started and stopped as needed - stuff like that. If all you need is to serve a long running process, linode and the like is more economical.
Backends are special App Engine instances that have no request deadlines, higher memory and CPU limits, and persistent state across requests. They are started automatically by App Engine and can run continously for long periods. Each backend instance has a unique URL to use for requests, and you can load-balance requests across multiple instances.