do mehapixels matter,? and of course why

A megapixel is the number of display elements on your camera's sensor. The more there is, the larger and more detailed your camera can potentially record an image. Sharpness still depends on a host of other factors such as optics, and ISO number. But to keep it simple, it all depends on what you want to do with the photos. If you only ever want 4x6 prints done then you won't notice if it's a 5mp or 20mp camera. If you want to make larger prints or display in a larger digital frame the photo will lose detail if the megapixels are too low.

one more benefits of high or very high megapixel - the tonal graduation of the image, that describes the smoothness of tone and colour blending in the image. simply, higher megapixel less contrasting.

for example, an image sensor of 4,000x3,000 pixels has x4 times capability of capturing tonal details than that of 2,000x1,500 pixels, simply it applys 2x2 times more pixel on defining the tonal graduation of the same details.

indeed, check the applications you need. if high megapixel just costs slightly more, go for it.

More megapixels is not necessarily a good thing, it is often driven by marketing rather than a search for image quality. Stuffing huge numbers of pixels onto a tiny sensor produces more noise at higher ISOs and can degrade the image such that you lose the benefit of more pixels.

I have produced lovely A2 size prints from a 10 megapixel camera with a large sensor; I couldn't do that from a 14 megapixel point and shoot camera with a tiny sensor.

Horses for courses. As a nature picture taker, yes because I use long lens and macro lens and therefore more MP gives me the ability to crop more and still retain file size.

It is the size and quality of the sensor that you should be concerned about most as this will determine the quality of the image. There have been numerous studies to show that cameras with a higher megapixel count provide poorer images if the quality and size of the sensor is low. This partly explains why semi-pro slrs will take much better pictures than compacts that can compete on the pixel count. A digital camera is a complex device, its important to resist the sales blurb of 'even more megapixels than the last compact' and look at its features in conjunction with one another. If the sensor is small and exposed on the body, you should look for something better. It's a very competitive market, and sometimes the rush to cram in the latest tech can have a detremental effect on image quality as a whole. A balanced approach which resists the sales blurb is best.

It would be more honest advertising to quote the pixels/cm²

rather than the gross number

but advertising never was very honest anyway.

I agree with hughden and deserted. Basically more megapixels merely means bigger images output. Marketing advertisement suppose that more megapixels means better pictures, but it's not necessarily true. For sure means bigger pictures but then many other factors have influence on the quality of your output. Surely useful if you go on big size prints, but it isn't the only detail to look when go buy a camera