I still can see them in system profiler, yet nothing on sidebar or desktop.
Checekd appropriate boxes on finder prefs...
ANYONE has any idea?
Is it may some some IOUSB file that got corrupted?
I am at a loss..
After tryng everything else, I tried re-installing the 10.6.8 update and the problem disappeared.
It would still be nice to know what made it appear in the first place.
Now I can read all my USB memory sticks/keys again, no matter how they are formatted, and even a USB mouse that seemed to be dead (see my other question) has started workig fine again.