The Engineering 7 Blog outlines enhancements made in newer solid-state disk technology that will improve user experience in Windows 7 significantly.  Because SSDs are essentially giant flash drives with no moving parts, there are inherent performance benefits in theory, however the blog discusses some of the lingering issues that the first generation drives are experiencing.  The article goes on further to say that not all SSDs are equal stating that the worst quality drives won’t best the performance of conventional hard drives.  Finally, as great as ideas of 100x performance increases in I/O latency sound, there are caveats that people should be aware of, specifically with certain types of I/O workloads.  Most SSDs aren’t well suited for database workloads when compared to existing enterprise storage technology, also there are long-term performance degradation concerns as the memory cells go through multiple write cycles. 

For more details and analysis, ComputerWorld has a great 2-page article covering SSDs in Windows 7 and implications on performance and features like ReadyBoost.