In a good system the memory card are always the weakest link, cheap systems and its a coin toss.
And sadly it don't matter much how expensive or kick ass brand memory card you get yourself, me i had reverse luck with some of my memory cards, so the best and most expensive ones i have gotten, well half of them ( 2 ) died before i even got around to fill them one time
but luckily their replacements have all performed just fine, and Amazon almost had a new card in my mail box before i got to send back the broken one.
I of course had many more regular memory cards die on me, but none as fast as those 2 U3 cards ( trancend and PNY )