Mongo is rarely the answer for high performance, high transaction systems. I use it quite happily to prototype applications due to it's very low boilerplate overhead.
If you need schema-less data storage in a "real" database, use PostgreSQL's JSON type.
But what about low performance, low transaction? Realistically the stuff I'd use it for wouldn't see much traffic. The big factor for me is schemaless. I don't want to create a new table each time there is an event with similar, but not exactly matching data between events. I mean, is MongoDB so bad that in any production setting the reliability is not there? Thanks for the link. I didn't know about the JSON type. Maybe I'll finally give PostgreSQL a try.
Most people who run into performance issues on Mongo are putting a lot of data into it. I've personally never had problems with it for side projects, but my tolerance for failure and data loss in those scenarios are quite a bit different than what most people expect out of production systems. It's definitely possible to use Mongo in production successfully, you just have to be aware of the tradeoffs and plan accordingly.
If you need schema-less data storage in a "real" database, use PostgreSQL's JSON type.
http://clarkdave.net/2013/06/what-can-you-do-with-postgresql...