I have a Lexar firewire reader for CF; also a Sandisk 12 in 1 for everything else; and recently I bought a 4 gig Sandisk Ultra SD card that came with this tiny little reader of it's own.
I thought it was just a nice bonus to carry around. But turns out it was necessary because, apparently, my older Sandisk 12 in 1 isn't capable of reading the 4 gig card.
Anyone know why? At first I thought it had something to do with the new card being too advanced to work with the ancient USB1 interface on my (equally ancient) Mac G4. But that's not the case because the new little dedicated reader works fine when running through the old USB1.