A megapixel is one million pixels, the more pixels in a picture the more detailed it should be. So theoretically the more megapixels in a camera, the better it should be. It is well known that most new photographers always set out to look for the highest number of megapixels for their money. But beware; an important feature is also the sensor size of the camera. For example, a 6 megapixel full frame SLR would most likely still take better photos than an 8 megapixel phone which would have a tiny sensor.
At the time of writing (1/3/2010) it is almost fair to say that brand new SLR cameras rarely are sold with less than 8 megapixels.