I mostly use Flask to create handy status dashboards and debugging tools for servers that do other things. It's a nice use pattern: you want to expose some of the internals of a server over a firewalled-off port, so you whip up a few HTTP endpoints in Flask, start an HTTP server in a background thread, and declare victory. It's quick and easy, and can save huge amounts of time later when you're trying to figure out why something isn't quite working.

There are other reasons to avoid GAE -- price, datastore latency, lack of flexibility -- but my main one is that GAE just doesn't apply to most of the things I use Flask for.

One thing I personally realised is that App Engine is absolutely fantastic for my needs, but as soon as my sites are outside of the free quota the costs rise extremely fast almost putting them out of price range before they even got started.

The other thing for me is that I have now spent time and invested hours into learning the App Engine platform but I get almost nothing in return since moving requires me to re-write or re-learn other tools anyway.

Unless I was a 100% committed to App Engine I don't want to launch a new project on top of it.

I'm definitely toward the novice end of the spectrum, but GAE scares me with how tightly coupled you can get to it, especially if you use libraries they provide.

It took a while, but I really like Heroku's workflow so far and I feel like I have to jump through a lot less hoops. For me, it's the perfect middle ground between buying and admining some ubuntu VM somewhere and GAE's deploy and hope it works style.

I was a big user of appengine in the last couple of years but have slowly moved off for cost reasons. It is a great service getting started, and scaled amazingly, but as the userbase grew, the cost became too much. There are certainly ways to mitigate it but for me it was not worth the extra time investment when it was mostly my side projects causing the problems.

GAE's working very well for me, i use flask on GAE.

I'm still bemused at how much of a free quota you get on GAE. I've had days with a few thousand hits, that doesn't even take any of my daily quotas above 35%.

No need to have to choose there -- you've been able to run Flask on AppEngine for some time now.

Apples and cucumbers. GAE is a platform as a service; Flask is a framework that can be deployed anywhere.

Unless I'm wrong about GAE...