Factors Influencing
Apparent Resolution:
Resolution is often quantified using "line pairs / mm,"
which is handy if you
shoot line pairs :-)
It's a lot more than just mega-pixels
When "resolution" is used as a term of quality, it is usually referring to "optical" resolution: the ability of the system to resolve real detail through progressively smaller areas of the image. By this definition, resolution is more than just a lot of pixels, it's a lot of pixels with distinguishable image data. Indeed, a 72 ppi file full of black pixels will have as much detail as a 300 ppi file full of black pixels - simply having more pixels doesn't result in improved image resolution. Resolution is the product of the entire camera system.

To illustrate, try this*: smear the front of your camera lens with lots of fried chicken grease -rub it in real good. Okay... now take a shot, look at it, and answer this question: how many mega-pixels will it take to improve the quality of this shot? Anyone care to test this?

* don't try this.