ReadyBoost:
1) It is designed to use USB flash sticks (1GB or greater in size is recommended) as mini pagefile's basically, because of their fast read/write access.
2) Readyboost has to stabilise (and needs at least 2-3 weeks for this).
3) It is basically an extension to Superfetch... where it creates a "Superfetch Store" on your USB memory stick. But the difference is that it is "persistent memory" whereas RAM isn't and if you reboot its contents is lost.
4) The cache file remains on the flashdrive when you shut down.
5) ReadyBoost is really good for improving boot-up times and general system performance. It does the former on any machine, even a machine running 1,000 tera bytes of RAM would benefit from better boot times. Once the system has booted though and its uptime increases the gains go away quicker the more RAM you have. And it's at this stage that ReadyBoost gets its bad press and people saying "just buy more RAM..." But the fact remains that ReadyBoost does help a lot with low memory systems, especially laptops.
6) Readyboost is not meant to replace additional ram, but to supplement it, especially in systems that are not always up (which are the majority of home systems in normal use).
7) Readyboost is a passive thing that helps in the long term, if you have a system which has been using readyboost for several weeks and you were to pull out the memory stick, the user would notice their system behaving differently. Most benchmarks compare things like FPS in games which has nothing to do with the purpose of ReadyBoost.
8) The question arises, if you have a 4GB USB ReadyBoost drive and set 2GB for ReadyBoost, will it be okay removing it everyday, once the PC is off to use at work/school? Or will it defeat the whole point?
The answer is quite simply that ReadyBoost is designed with this in mind. The fact that it lets you allocate a certain percentage of the drive, and that you can "unplug" the drive at any time provides a hint to users that ReadyBoost doesn't tie/lock the drive down to that machine.
Obviously when it is unplugged from your Vista machine it will reduce the performance. But as soon as you plug it back in... the performance increases again!
Space needed - min. 256 MB, max 4 GB (because
ReadyBoost can compact this data this can yield up to 512 MB and 8 GB respectively), recommended, ratio 1:1 to 2.5:1 (2 GB RAM would be 2 GB - 4 GB of flash drive).
How many drives can I use? - One
Security risk? - No, the data is encrypted.
ReadyBoost FAQ
ReadyBoost Compatibility List