Nikon D3100 Memory Card?

Apparently the size of the memory card matter to a camera as it can slow it down if the card is too big.
Any idea what size/ the best the memory card is for a Nikon D3100?

Added (1).… Size of the memory card matter to a camera as it can slow it down if the card is too big…
A salesman told me from Future Shop

I don't know where you heard that a large card slows down how fast it can read or write, but that is not true. The Class of the card determines how fast a card can read and write.

Now what IS true, the larger the card, the longer it takes for all the image files to be copied to your computer.

This is one reason I use cards that are no larger than 4 gb. The 4 gb card is sort of cool because I can copy all the image files to a separate file folder for each card and then make backups on a DVD without any need for further post production.

If you plan on shooting video, buy Class 6 cards for HD video and Class 10 cards for shooting Full HD video.

David is correct. I shoot with an eos t1i and I use only 8gb / Class 10 - the fastest card out there right now.