There's a whole group of people saying that "megapixels don't matter" ... well, or at least there is Ken Rockwell.
If MP didn't matter, then what is the bottom of acceptable physical resolution? Why isn't there these high end cameras that take tremendously sharp images at 640x480 resolution? Heck, at that size, you'd practically be able to SEE the individual sensing elements on a full frame camera! Just imagine the low light performance!
The problem with this is is that physical resolution does in fact matter, just not in the way that you might think. For example, my 12.4 megapixel a700 has similar optical resolution, despite having about 10% fewer sensing elements than my a350. In fact, in practice, if you scale an image from the a700 to 14.2 megapixels, they look exactly the same, similar in sharpness, similar edge definition.
However, if I took a 6mp image and scaled it up to a 12mp image, it won't be as sharp as an image taken with a 12mp camera. So there is a limit to how much you can realistically say "megapixels don't matter", because a 12 megapixel camera does record more data over the same space than a 6mp camera.
Now, a 6mp image may appear sharper if printed at 300ppi without any interpolation, mostly due to optical flaws. But it will also be smaller than a 12mp, 300ppi image. The 12mp image will likely appear slightly softer than the 6mp image, but not as soft as if you scaled up the 6mp file to match the size.
OTOH, smaller resolution means larger light sensing elements provided that the format is similar, and if you were to compare like-generation cameras the lower resolution camera will have better noise performance.
So, no - megapixels don't "matter" but only to a reasonable extent.