Well with AMD offering no competition, Intel is going back to the old days of $1000 prices for their new top-end CPU.
The 3.2GHz i7 (Nehalem) will launch at $999 while the current top-end Core 2 Duo - the 3.16 GHz E8500 - is now $183.
The Q9100 costs the same price as the current X9100 3.06GHz model in the iMac and will have similar TDPs, so it is probable that Apple will offer it as a BTO option soon after launch for the same price as the 3.06GHz model (or get an extra $100 in raw profit because it's a quad).
The Q9100 would also match the price of the 2.6GHz X8700 available as a BTO option on the MacBook Pro, so it too might become a BTO option for that model.
However, I expect Intel to drop the price of the X9100 and the X8700 (why sell a dualie for the same price as a quad?) so Apple might make the X9100 and X8700 as the base CPU for the iMac and MBP, respectively, and then offering the Q9100 as a BTO extra-cost option for both.