We use MongoDB on ww.interstateapp.com but only really because Interstate started out as a small fun project and not something we expected to take that seriousl

We use MongoDB on ww.interstateapp.com but only really because Interstate started out as a small fun project and not something we expected to take that seriously (so it didn't matter too much if MongoDB was a perfect fit or not - it turns out that it suits the app quite well). If your app is the type of application that would benefit from the advantages of having a NoSQL style setup (not all do) then go for it but I can't see MySQL being phased out (in terms of usage by devs, etc) anytime soon... Also, if you don't know whether your app could benefit from using MongoDB it's kind of a general rule of thumb (from what I've seen) to just go with a traditional MySQL setup for now.