Used properly, however, a SSD will last forever. Typically, the drive will include load spreading somewhere in the chain. The algorithms are a bit more clever than what I'm about to describe, but naively, if you've written the same location more than a few times, you move that data to a different location. This are often implemented in the drive's firmware, but may also be implemented in the file system (Linux comes with a few flash file systems that do this -- indeed, OLPC uses one of them). Used this way, the solid state drive will last for many decades of continuous use before failing, and will eventually fail for the same mechanisms as any other old IC. A 40GB drive, written at 100Mbps, will take about an hour to overwrite completely. With an endurance of 100,000 cycles, you get a bit over 10 years of continuous write at that speed before you run into endurance limits. With normal write frequencies, that means it'll last essentially forever.
Data is stored as charge on a conductor surrounded by insulator, but the insulator isn't perfect, and eventually, electrons do drift on and off. As a result, data stored in flash has a lifetime on the order of 10 years if it doesn't get refreshed. Of course, refreshing it is trivial (read out data, write it back).
Of course, with a Sony laptop, the major question isn't drive lifetime, but how long until the hinges or latches break. Sony laptops typically frequently have mechanical failures within a few months of purchase. Sony skims on quality quite a bit, these days, and is mostly running on reputation for quality acquired many years ago. That, combined with shooting for the lowest possible weight (and skimming on construction quality to save weight too) makes for pretty flimsy laptops.