Yes, it was overhyped (and is underhyped now, at least on HN). Yes, it has its problems. Yes, it is not correctly positioned in people's minds (web-scale? not really). MapReduce on top of MongoDB, in a single-threaded JS engine - are you kidding me??? But it is useful tool nevertheless; one I am happy to have in my arsenal.
MongoDB will NOT solve your scalability problems. Old news. It will even add some of its own problems on top of it. But man, is it nice to just fire that data into your database and forget about DB-level schemas... And when you need that data, it is just there. True, I have built an ORM on top of MongoDB so it manages the DB for me; but it was easy to do and is incredibly useful. I would have done it with MySQL too (actually, I did - and it was a PITA to build because of relational databases' rigidness).
So please, stop bashing MongoDB for wrong reasons. It is an excellent and easy to use storage - when used for the right kind of problems. Nothing more, nothing less.