I (obviously) disagree. Reinventing the wheel is fun, we all do it. But (to stretch an analogy), if there have been cars for decades, and you claim to have just invented the wheel, and that all previous wheel were square, then I would ask what you (think you) have accomplished - why not a) make a better car and b) tell us why your car is better. If the MongoDB schtick is "we can do 10% of what Oracle can for 1% of the price" then that's great, there is a real market for that (assuming that 10% overlaps with the 10% of Oracle that you happen to use).
I was using MySQL for real work back in the 1990s. I remember then, them saying, you don't need foreign keys - just check it in your application. You don't need transactions either, just handle failures in your application, yadda yadda. And of course, MySQL these days supports all these things (with InnoDB, an Oracle product) because these things weren't there "for lulz" in commercial databases, they were there because people needed them and saw value in them. Now I am getting a complete sense of deja vu with MongoDB. It will have to add transactions. This is inevitable. It will have to add enforced schemas, row level locking, ACLs, and other features besides. If we remember, then in a year, let's touch base again, and you'll see I'm right. This is what I mean when I say the lesson of MySQL.
And in 10 years, there will be another product, let's call it ZongoDB, and the cycle will repeat again. You don't need this, you can't do that, they'll say, and the MongoDB crew, by now themselves old geezers (this means, in IT, in their 30s) will roll their eyes.
PS I may be an Oracle partisan, but I recognize too when Oracle implements something IBM did back in the 70s...