For anyone who has a Nikon DSLR, have you had any problems with it?

I'm looking into the Nikon D3100 and wondering if I should purchase the warranty.
BQ: I'm buying this SLR with a 16GB Ultra SanDisk memory card, how many pictures can it hold? And what's the difference between Ultra and Extreme?
Thanks for all the answers!

Added (1). The sd card that comes with it is class 4, what's the difference? :/

Added (2). Oh, it transfers the files faster. Why does that matter so much?

I have had my Nikon D40 for 3 years, and have experienced no problems. My dad has had his D3000 for ~4 years and has not experienced any problems. Our family friend has had his Nikon D300 for ~4 years as well and has had no problems with it

Warranty may be a good idea if you or the people handling the camera are prone to accidents. I didn't purchase any warranty because I put protecting my camera as a higher priority than receiving a flesh wound

Ultra and extreme are just marketing names, what is important is the class of the memory card. If you are looking to do video with the D3100, get a Class 10 card at the minimum. As for pictures, 16gb can hold a couple thousand

remember to upload pictures after each day of shooting to make sure that the pictures are secure on your computer

a class 4 card transfers files at least the speed of 4mb/s. When shooting HD video, the data stream is huge. A class 6 will have trouble keeping up, therefore a class 10 is needed.

Imagine you are in a classroom with a professor that talks very fast and never repeats him/herself. Are you better off learning how to write very fast, in which case you can take notes on the material and get a good grade? Or do you write at a slower speed which makes you skip important parts, thereby lowering your grade.

I have been using Nikon cameras, 35 mm SLR since 1970 and Nikon dSLR's since 2002 with NO problems.

Using huge memory cards like the 16 gb is a mistake. Never will you fill such a card in a shooting day and the proper method of managing your image files is to copy All the images you produce in a day to your computer and once they are safely on the computer, format the card using the format feature on your computer. Better to have four 4 gb cards than a single 16 gb card.

Unless you plan on shooting a lot of video a class 4 card is fast enough at writing and reading image files. Class 6 or Class 10 cards are only necessary when shooting video.

The time it takes to transfer image files from the memory card using a card reader is much faster than trying to use the USB cable from camera to computer. A full 4 gb card can take up to 15 minutes to transfer the images from a 4 gb card to your computer using a USB 2.0 card reader, much longer if using a USB cord (no longer included by many camera maker for just that reason).

Using a ExpressCard54/CF card reader, I can copy a full 4 gb card to my computer in less than 5 minutes.

My son has one. He usually complains about the low maximum ISO and the non-zooming preview. It's limited to the D50 I think being an entry-level dSLR.

Faster file transfers allow for faster shooting. The importance is more evident when doing video.