I have a new 8 GB memory stick and it passed the readyboost test - initially. But I wanted to dedicate the device to readyboost so I reformatted to NTFS (was FAT32 initially) and now all I can get is "This device cannot be used with Readyboost". I have tried a command line test that gives me a read speed of 4.8 MB/S which according to the specs I have seen is fast enough for Readyboost.