The man himself says this is possible: http://stackoverflow.com/questions/7727358/deployment-of-mahout-on-google-app-engine
Going to start an experiment now if you want to join me.
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Here's what you'll need:
1. AppEngine SDK: https://developers.google.com/appengine/downloads#Google_App_Engine_SDK_for_Java
2. Read through AppEngine Docs (getting started in JAVA): https://developers.google.com/appengine/docs/java/gettingstarted/
3. AppEngine new project template: http://code.google.com/p/googleappengine/source/browse/trunk/java#java%2Fdemos%2Fnew_project_template%2Fsrc%2Forg%2Fexample
4. Mahout (latest stable release): https://cwiki.apache.org/confluence/display/MAHOUT/Downloads
5. Include Mahout Recommender code only (since MapReduce is not yet supported on AppEngine, those types of jobs still need to be run on AWS or locally): https://cwiki.apache.org/confluence/display/MAHOUT/RecommendationExamples
- suggest using "ratings.dat" from MovieLens, since all training data is contained in one flat file...
That's it, I'm trying this now will update here when I've made some progress. Again, this should all work in theory, but in reality there's bound to be some gotchas.
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UPDATE #1 - A tutorial that seems to be attempting the same (in Japanese): http://orfeon.hatenablog.com/entry/2012/07/01/002300
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UPDATE #2 - Maybe Google's Compute Engine could also be used as a cheaper alternative to EC2, but I'm getting ahead of myself: http://cloud.google.com/products/compute-engine.html
Running Mahout on AppEngine 