Tommo, the megapickle arguments will always rage with the particular sensor design ( Foveon ) that Sigma use.
Basically the way to look at this particular one is to look at the sensor dimensions ( 23.5x15.7mm ) which is pretty well in line with most APSC sensor sizes as a 3:2 ratio or 1.5 crop of 35mm frame format.
Then look at the total number of pixels ( horizontal x vertical ) in the sensor ( 4,800×3,200 ) and then multiply the two to get the number of megapickles that the sensor actually has.
This gives you a bit under 16 megapickles under the way thateverymost other manufacturers quote their cameras as. The difference with the Sigma sensor is that they claim each photosite on the sensor measures colour channels separately ( RGB ) so therefore you must multiply the total megapickle count x 3 giving somewhere around 46 megapickles.
The actual pixel density of that sensor is really no more than the current class leading Pentax / Nikon designed by Sony sensor in the K5 / D7000 but it it simply interprets things differently.
Yes, the sensor and design do work well, but do they work 3 times as well as the rest both price and performance wise?
Only time and the market place will provide that answer.
Sadly I think it will be a rather resounding no on the price issue alone.
Edit --- I really would be quite happy to be proven wrong on the acceptance of the Sigma in the market place, maybe it will be the silver bullet but going on the past models that have failed to set the world on fire I really can't see much more than a soggy match head with this one. Please prove me wrong Mr. Sigma.