A group including Intel, Dell, IBM, and EMC is collaborating on a standard for PCI Express-based solid-state disks. Ars Technica has the skinny on the group's plans, which aim to define a standard connector and form factor for PCIe SSDs. It looks like the consortium is leaning toward sticking with the 2.5" form factor commonly used by modern SSDs, which strikes me as a little odd considering that PCIe-based models generally reach their jaw-dropping performance levels by combining multiple SSD controllers and flash chips in what are effectively multi-drive RAID arrays. Good luck cramming all that into a 2.5" drive.
According to Ars, the group is actually hoping to migrate all solid-state disks from Serial ATA to PCI Express. That might seem unnecessary with 6Gbps SATA delivering more than enough bandwidth for today's fastest flash arrays. However, SATA controllers are usually found on I/O hubs one hop away from the CPU, where they must share interconnect bandwidth with other peripherals. The Serial ATA protocol wasn't designed with solid-state storage in mind, either; a custom-tailored standard riding atop a PCI Express interface could offer better performance even if the PCIe link doesn't have any more bandwidth than its SATA counterpart.
The prospect of an ultra-fast SSD plugging directly into PCIe lanes on the CPU is certainly tantalizing. As Ars astutely points out, we could see even greater benefits if operating systems more intelligently used the solid-state storage they have available. SSDs seem best suited to their own tier in a system's memory hierarchy—as fast scratch disks and repositories for one's most commonly accessed files.