I'm disappointed that the support will be only for the X3400 series cards in the initial launch. I don't know if this is a driver issue or chipset implementation issue, but later in the year, ATI will come out with hybrid Crossfire boards that support higher end cards like the X3850 and X3870.
The improvement with an X3450 with hybrid Crossfire enabled is listed as 60%, and any improvements with a midrange part like the X3850 should be much less, perhaps closer to 10-20%.
Still, I have an ASUS 690G board right now and I'm not averse to putting a midrange GPU on what is essentially an ideal entry level or HTPC board. I'm a CRPG gamer but I'm budget conscious. I don't use multiple monitors, and I'd really prefer getting some use out of the integrated GPU, even when I choose to buy a better graphics card.
Still, if my budget fails me in February, I just might give this a try instead of just getting an X3850. What I'd also like to see is three way hybrid Crossfire, two X3470's or X3850's alongside the IGP. Add in Fusion in 2009, and it will really get interesting.