If you want an experts view of the currently shipping crop of PCIe Flash cards, here is a great survey from the blog makeitfaster.
A chain of press releases from Flash memory product manufacturers has led me to an interesting conclusion. We already have Flash caches in the datacenter. How soon will they be on the desktop? Intel’s SpeedBoost cache was a joke compared to Fusion-io’s PCI cards. What might happen if every computer had no disk drive, but used a really high speed Flash memory cache instead?