ahaha Will, that's hilarious, have they learned to strike that pose every time?
this is a very interesting observation. i once read 4 megs the right size for these sensors. cramming in more means they must have to process the heck out of them. the new cameras do work faster, but as for image-quality, i really wonder.
Others say
6 MP are perfect (cached copy, site is broken now), but my comment wasn't about noise, more about other qualities of the image.
Almost all my IXUS v2 images look dull and very soft, while newer cameras do a better job at sharpness and "punch", by tweaking (just my wild guess here) contrast, colors, etc in-camera. And the same treatment done in PP can give some life to an image which otherwise would be quite dull.
As for noise, I am in the league of those who don't care that much. These high-MP images aren't meant to be viewed at 100% crops, they are always scaled or printed at reasonably high DPI, where most noise becomes invisible (never mind the fact that, still, my LX2's sensor is about twice as large as the IXUS').