I was lazy when I received my Note 2 and used a super slow card from an old phone with all my music and photos on it instead of the card that came with the Note 2, Sandisk class 2 or something crazy slow from a Blackberry. When I would shoot video or take a few pictures weird things like loosing pictures would happen quite frequently.

After I upgraded to an Sandisk ultra I quit loosing pictures and shooting lagging video. Because of all the problems I had I did format the new card in the phone but since I have used any ultra card without a problem.

If the card is too slow, it will cause issues. I still use the old slow card in another device with no issues. The ultras ROCK!