ATI posted a link to a DX10.1 whitepaper on their forums. Since it is not on the front page and references the 3800 series, a name not yet 'official', it probably wasn't meant to be posted. Grab it while you can here and here.
There is a nice table on pages 4 and 5 lining up what the additional .1X adds, and then a few pages more of explanation. It looks to be a good primer on DX10.1 and a bunch of the tech it brings. If you are hardcore into graphics, it probably will not go over your head.
For the average techie, it is a worthwhile read though, and should save you from getting the info piecemeal. Grab it before it is pulled.
DirectX, DX10, Whitepaper, Technical Note