Do not trust anything it does implicitly (like casting stuff, running triggers reliably, locking properly etc).
Nothing follows logic so if you assume something would work a particular way, it will most definitely do the wrong thing instead.
It is fine otherwise.
In a serious tone, I ran large apps on MySQL, it works and performans fine. But makes it easy to shoot yourself in the foot. Go with PostgreSQL if you can choose / it is not a big hassle.
