Rev Vista with ReadyBoost
ReadyBoost is a new feature in Vista which allows the user to accelerate the performance of the PC simply by inserting a USB Flash Disk/Pen/Dongle/Widget. It uses the fast flash memory instead of paging files back to the sluggish hard disk which greatly speeds up the operating system.
I've just been reading a great Q&A from the guy who owns this feature in Vista and one of the things that caught my eye was the ratio of system RAM to Flash memory that is recommended for the biggest performance gains.
He recommends when your machine has a small amount of memory - which might be 512MB in today's machines - you should use a ratio of 1:1; so effectively a 512MB USB flash disk. However when your machine has more memory (mine has 2GB), then you should try a ratio of 2.5:1 (RAM:FLASH), which would mean a flash disk of 800MB would be ideal for my laptop.