This is by far the fastest flash drive I've owned. I haven't tested the quoted speed but from what I've seen it's fair enough to say it's quick. Readyboost enhanced means all areas of the drive meet a minimum speed required for Readyboost and with 4GB I was able to allocate half to vista's Readyboost. Doing this however can cause problems with the U3 software, if you use both technologies together you may stumble across some stability issues or you might not be able to eject your drive at all. Some have confused the Readyboost and U3 software in the reviews and it is very easy to remove or replace the U3 software from the drive if it comes to the worst. Just hit the launchpad enter the settings select the uninstall tab and go through the wizard, easy as pie. If the U3 software was ironed out to alleviate those bugs with vista and Readyboost then this would easily achieve 5 stars.
Notes: U3 is not compatible with non windows OS so using a password on the drive can completely lock it from operation under another OS.