I use the Alpha 100 and love it!
It can be had for about half the price of the new 700. There doesn't seem to be much on the new Alpha to tempt me to want to put out another grand when the one I have does everything I need it to.
About the sony sensor, it is not only in nikons, and has been for a while, but it is also in one of the other leading brands...can't think of which one right now.
I have been using sony professionally since I went digital back around 2000, as soon as they came out with the 707. I can't say enough good about them, and from what I hear they also seem to have the best battery life....
think I will go look at the test shots and see if I need the new Alpha......