I bought a new digital camera a few weeks ago, and I was very impressed by its resolution - a whopping10 Mpx! (10 million pixels). But that is tiny compared to the digital camera involved in the University of Hawaii's Pan-STARRS project...
Their digital camera is a staggering 1,400 Mpx!
I would have to buy another 139 cameras to compete with that!
Pan-STARRS main aim is to repeatedly photograph the sky looking for potentially hazardous asteroids - we only know of 953 PHA's at the moment (according to SpaceWeather.com). Having said that, they will also be able to do lots of other interesting science as well, such as looking for variables stars (e.g. supernovae).
This project continues in the great tradition of astronomers leading the way in digital camera technology. The first CCD (a type of digital camera sensor) was used on the Kitt Peak National Observatory's 1m telescope all the way back in 1979. This CCD was 50x more sensitive than film. It took until 1990 for the first commercial digital camera became available, and now, almost everybody has one!
For typical DSLRs, 21 is the highest, and many many still are being used everyday for all sorts of purposes, including pro level shooting at 8 - 12. In between that are your 15-16 creatures. I believe medium format capture backs have already gone up to 40 and 60. I may be outdated about these figures and at any rate, I personally don't usually have a need for larger MP sensors in a 35mm DSLR size/format.
Yes, currently the Sony A900 has the highest MP count. Depending on how much you need to crop, what size you need to print and how much details you can sacrifice, a 6MP cam is more than sufficient for general use.