higher class simply means higher minimum read rate(class 2- 2mb/sec, class 8 - 8mb/sec etc) so it depends on what you use it for. If playing high bit rate videos or copying large files you will definatly notice difference between class 2 and 6, for most apps you will not notice any difference(unless its a GPS nav soft with preloaded maps or comparable "big ones"). Most cards work higher than what they are rated for though(my personal experience with most sandisks) and some cheaper do not work at the class they are advertised at(no names), only way is to test the card you get and/or read reviews for the one on sale
