just thought i would make my 1st post here semi-useful. recently bought a sandisk sd card which was very slow, copying files failed sometimes and was generally crap performance wise.
turns out (after about an hour of thinking, this isnt right) it was the cheapest possible memory all (properly) badged up and boxed as sandisk.
few things to look for, if you didnt already know...
lock switch - should be white, this was yellow.
card shape - there should be a notch on the base, not just a flat card
warranty - should say limited lifetime warranty, not lifetime warranty.
printing on box - for the ultra II, the II is normally at a different height on fake boxes
serial number - should be on the back of the card in white near the bottom edge with serial as BE##########B and then made in china, not just a generic number printed on the box (tho some new fakes are halfway clever to putting serials on)
according to ebay 80%+ of sandisk ultra II's sold on there are fake. why they bother allowing any to be sold is beyond me

but dont get stung by buying one off there as performance is shocking