According to "...Matt Ayers, who is the Program Manager in the Microsoft
Windows Client Performance group and basically owns the ReadyBoost
feature...
Q: Why don't you support SD on my USB2.0 external card reader?
A: We unfortunately don't support external card readers - there were some
technical hurdles that we didn't have time to address. In general, if a card
reader shows a drive without media in it (like a floppy drive or CD ROM
does), we can't use it for ReadyBoost.
SO theoretically you cant use card readers for CF or SD cards...but some
people here have gotten it to work. Probably how "hot swappable" the driver
is for the reader. I have an SD card "carrier" that shows up to ReadyBoost,
but my CF card reader does not...
This info is from Tom Archers Blog where he interviews
Matt..
http://blogs.msdn.com/tomarcher/