Well the other thing is: people act like migrations are the devil. Yes, moving your data from Mongo to PgSql, MySql, MSSql, Oracle, etc. is going to be difficu

Well the other thing is: people act like migrations are the devil. Yes, moving your data from Mongo to PgSql, MySql, MSSql, Oracle, etc. is going to be difficult. However: why start with a production level Oracle install anticipating "web scale" when you're not going to have more than ~1k users at launch. People look to Google and Twitter and Facebook for advice on how to scale. They then apply this advice far before they need to. I don't think you should plan to be large scale from the get-go. I think you should have a plan for what you're going to do if you get big. My $.02