I know all details about how entity groups work in GAE's storage, but yesterday (at the App Engine meetup in Palo Alto), as a presenter was explaining his use of entity groups, it struck me that I've never really made use of them in my own GAE apps, and I don't recall seeing them used in open-source GAE apps I've used.
So, I suspect I've just been overlooking (not noticing or remembering) such examples because I'm simply not used to them enough to immediately connect "use of entity group" to "kind of application problems being solved" -- and I think I should remedy that by studying such sources with this goal in mind, focusing on what problem the EG use is solving (i.e., why the app works with it, but wouldn't work or wouldn't work well without it).
Can anybody suggest good URLs to such code? (Essays would also be welcome, if they focus on application-level problem solving, but not if, like most I've seen, they just focus on the details of how EGs work!-).