Not often. Platter drives fail a hell of a lot more. I've had one SSD die on me in about 3 years. In the same amount of time, I've had, oh, what would you say, Peter, about 300 hard drives fail? Granted, the SSD that died was consumer grade, and the HDDs were mostly enterprise, but that's not a great sign. None of the enterprise SSDs failed.
To compare apples to apples, we had to have the hard drive in my wife's old Macbook replaced 3-5 times over 3 years (and the HDD in my Macbook Pro at least once). The SSD I had that failed lasted for about a year.
