I bought a new USB stick specifically for ReadyBoost and it failed the test. Testing data is available in the Event Log. There is a way to force a device to be used anyway.
From Windows Vista Magazine:
Using the left-hand pane, work your way through the following folders: HKLM (Local Machine) -> SOFTWARE -> Microsoft -> Windows NT -> CurrentVersion -> EMDgmt. You'll have a list of USB devices the computer has encountered, one of which should be your USB stick. Click on it.
Here there's a few details you need to edit. Double click on Device Status and change the value to 2, then ok. Do the same for ReadSpeedKBs and WriteSpeedKBs, changing their values to both 1000. Exit the regedit and breathe a sigh of relief.
A few notes:
- The values should stay in hex.
- My drive just barely failed the read/write tests. A very slow drive will have negative impact on performance.
- This is a hack, so do benchmarking to make sure its actually improving things.
I had another stick that is several years old pass on vista launch day but fail today. I suspect either something changed with the stick (unlikely) or Microsoft upped the speed requirements with a patch?