It came to my attention that German Image Engineering launched 6MP web site telling there is no need in having more than 6MP in comact digital cameras, as image quality becomes worse at higher resolution. The basic claim is that 3um pixel is the optimal pixel size for compact digicams, thus the maximal resolution should be 6MP for 1/1.5" sensor.
One problem with this approach is that technology is progressing and what used to be true a few years ago, might not be true tomorrow. For example, pixel binning, if made correctly, can dynamically scale resolution and effective pixel size.
Talking about low-ISO pictures, a high full well capacity is important to get noise free pictures. Historically, smaller pixels had low full well. But there are few solutions in works to provide a dramatic improvement here. Also, various HDR modes should make small pixels more attractive, to some extent.
So, it might be true that the old generation 3um pixels are close to the sweet spot for compact digicams. I'm less sure that this statement remains true in a few years from now. Among other things, it depends on when compact cameras switch from CCD to CMOS sensors, as most of these solutions are inavailable in CCDs.