The Sony a850 represents a landmark camera. This is the lowest price full-frame DSLR ever offered. It will sell for around $2000 for the body only and for around $2800 in a kit with the new Sony 28-75mm f/2.8 SAM lens. The only differences between this camera and the a900 is the viewfinder: a900 with 100% view and the a850 with a 98% view; and the shooting rate: a900 at 5 fps and the a850 at 3 fps. Otherwise, they share the same 24.6 MP sensor and the same dual BIONZ processors. Most of the other features of the a900 are carried over to the a850.
Considering that most other "entry level" full-frame cameras, like the Canon 5D mark II and the Nikon D700, sell for the price of the a850 with a lens, this is a great deal. Like I've said before, Sony is the company to watch out for in the years to come. I bet it won't be long before we see a full-frame DSLR for around $1500.