A couple of days ago PC Perspective published an analysis of the long-term performance of Intel's mainstream solid state disks, you can check it out over here. The article claims the performance of solid state disks, like the Intel X25-M that was used in the test, degrades over time due to internal fragmentation.
Intel responded to the article and stated they were unable to duplicate these results:
In response, Intel made a statement on Thursday. "Our labs currently have not been able to duplicate these results," Intel said. "In our estimation, the synthetic workloads they use to stress the drive are not reflective of real world use. Similarly, the benchmarks they used to evaluate performance do not represent what a PC user experiences."
Intel continued. "In general, when a PC's drive (SSD or HDD) is full, there will be some reduction in system performance, however the performance reduction reported by PC Perspective is higher than we generally expect, which is why we are looking into the methodology."