The analogy goes like this: If you're very rich, you can do horrible drugs and pay a veritable army of people to keep you presentable and working. Of course, this until one day it doesn't. Being large and successful doesn't mean that there's nothing festering deep within. Companies and people can become so invested in previous solutions that the perceived benefit versus the cost of switching is almost always too low to gather enough political will to execute. MySQL is a drug, when you start it is cheap and available, but as you grow as you hope you will, you start to need more and more. Of course, this exposes many of the flaws and problems of the drugs you were on and if you're in a bad way, still are. Better to go through a bit of pain now and know what you're in for than to just use MySQL because facebook, twitter, amazon, and flickr can pay a huge team of people or large consulting firms to make their technology decisions actually work. If you really must, use MySQL to spike the product but know the side-effects and know when to get the hell off it.