Anyone knows how much does the speed of SD cards matter to your phototaking experience. And when does it make a difference. I read somewhere that high speed SD cards (10MB/s) matters for taking photos in higher megapixels (large size).

My question is, will it makes a difference to cameras that are only 3megapixels?
And any advice for purchasing a 128/256MB sd card? go for the cheaper one since no difference?