Have a look on the back (or front) of the card. Is it made in Taiwan or Japan? If in Taiwan, then the cards are not as good as those made in Japan. The speed of the cards are not as fast. Had a Kingston Taiwan in my N70 and took forever for it to load up the gallery etc (altho it didn't jerk on movie recording), but the Kingston Japan card in my N73 is great.
It could also always be a firmware issue, have you upgraded to the latest? If not, give it a go...