I recently discovered that the brand of SD card you use can make a huge difference to your camera's buffer. I used to use a no-name-brand 133X 4GB SD card, and at the most I could only take twelve pictures at 2.5 frames per second before my buffer would die out on me. The buffer, in case you didn't know, is a temporary storage area in your camera's circuitry that "holds" pictures in memory so that your camera has enough time to write your images to the card, and at the same time it allows you to continue taking pictures as it writes to your card.
Well, after my little discovery that brands could make a difference, I went out and purchased a Sandisk Extreme 3 2GB card. And low and behold I pushed my buffer's limit to 100 images at 2.5 frames per second! What a joy to discover that I could take 100 images within 40 seconds. Although that sounds impressive, compared to higher end cameras like the D700, it's actually quite slow. I believe with the Nikon D700, you can reach a top speed of 100 images in 12.5 seconds. That's fast! And such speeds are often used only for actions/sports photography. For my purposes, 100 images at 2.5 frames per second is sufficient.