What makes a camera professional... and expensive?! Is it worth it??

The Nikon D3000 is less than $500.00
The Nikon D3 is more than $5000.00
That is more than 10X more expensive!! What makes a camera worth that much more you ask?!
Well, here is a short and simple list :)

Physically the camera looks and feels different.
-First of all better, cameras are physically bigger, this make them a little easier to manage with bigger lenses and flashes attached. Also, it is easier to hold a bigger camera more steady because your hands have more to hold on to.
-More expensive cameras are usually made of magnesium alloy, this makes them a lot lighter than other metals and stronger than plastic.
-They are weather sealed, which means they can be rained on or snowed on and survive (this DOES NOT mean water proof) Also, it helps protect against dust and dirt.
-There are more buttons, dials, and knobs on full frame camera. This makes it easier and faster to change your settings. You don’t have to go “menu diving” to change your white-balance or ISO for example.
-The LCD screen is bigger and a higher resolution so that you can examine the exposure and composition better.

The sensor and the image processor is what really makes the difference
-The first thing is that nicer cameras are full frame. A bigger sensor doesn’t necessarily mean better pictures, but generally full frame sensors have the following characteristics...
-The image processor is faster, which means that instead of shooting 3FPS (frames per second) you can shoot 9 or even 11 frames per second!
-The sensor has a better dynamic range; which basically translates to images that have more contrast and are sharper.
-Another huge advantage of a nice camera sensor is that you can turn the ISO up higher and shoot in less light without as much noise. A cheaper camera might be able to shoot at an ISO of 1600 where a nicer camera can shoot with an ISO up to 12,800 without losing image quality.
-There are more auto focus points, which means that the camera can focus on things that aren’t directly in the middle of the frame. My first Nikon has 3 auto focus points while the D3 has 51!
-Notice that I said NOTHING about megapixels! There are some point and shoot cameras with nearly 20 megapixels but one of Nikons best cameras has only 12! The reason for this is that the more megapixels, the lower the ISO has to be and the less frames per second. Megapixels are not that important unless you plan on printing your pictures to go on highway billboards!

Is it worth it?

Not everyone needs a $5000.00 camera, honestly, not everyone needs a $500.00 camera either.
If you don’t know how to use all the bells and whistles on an expensive camera and you're not shooting in the rain or near darkness everyday, then you are just fine using an easier to use, cheaper, and smaller camera.
If you are going to shoot on auto all the time, you probably don't even need a DSLR at all.
Just because your cameras lens can be removed does not mean your pictures will be better.
Before purchasing any camera, you need to think about what you will be using it for and do some research. Many point and shoot cameras are much more practical and take just as good of pictures if you plan on shooting in auto all the time.