Many of us do. Being tech lead of 1:many support, a big chunk of my work is to develop (and code-review, advise on, debug, etc etc,) software for internal consumption, and the vast majority of it is on App Engine (in Python) -- which I love, because the whole circle of software development (esp. with Python!-) is my top skill and passion (close behind is technical writing... esp. about Python!-). (If you wonder how I ended up in support -- after 10+ years with Google I was sniffing around for new challenges within it, and, partly based on my reputation on StackOverflow, one of 1:many support's key channels, I was offered this opportunity).
My love story with App Engine goes back to before it was named that way, much less offered to the public -- back then, early in my Google years, it was a 20% project nicknamed after a Greek mythological figure. Not close to my job back then (I was uber tech lead, Production), nor could I scrounge more 20% time (I was always spending all of my 20% in other tasks), but I heartily encouraged my reports, direct and indirect, to fully take their 20% -- and to use it to help what would later become App Engine. I always supported it whole-heartedly, including urging my friend Guido van Rossum (Python's inventor) to join that team when he spent some years at Google (of course his contributions were on the Python side of things!), and using it for any project that would fit (I also originated the hooks-based unit-testing approach that later matured into what's known on the Python side of things as the `testbed` module).
To this day, I still find it the best platform I've ever developed for (with the possible exception of early Unix versions, BSD 4.3 included but System V excluded, before the hockeystick curve in complexity that kicked in around that time -- but back then I developed in C and TCL, so, counting the language as part of the platform, App Engine still wins:-). Modules AKA services, and the ability to run different modules with different scaling features and machine sizes, are really game-changers within the App Engine world, from my point of view -- it's getting better and better! Don't let me get started on Flex Runtime and how you can make up an app with one or two modules in Flex and others in standard runtimes, including in different languages...
My current Director Luke Stone, in his recent post
https://cloudplatform.googleblog.com/2016/04/why-Google-App-Engine-rocks-a-Google-engineers-take.html , was kind enough to credit me as "a friend" who helped convince him to try App Engine to deploy apps -- he's now in charge of all of Google Cloud Platform support (which is how and why I now report to him). As a Director I suspect he doesn't get anywhere as much time to develop software as, engineer to the core!, he'd crave to have, but, when he DOES do development -- App Engine is there for him, better than ever.