If they are truly planning this for the MacBook, then they are surely planning to bump the iMac to this chip too or better the Conroe. They continually refer to the MacBook and iMac as their "consumer line". I have been planning to buy an iMac for some time now, and this is definately an upgrade I would like to see. I'm most likely waiting until after MacWorld Expo to see what updates they will have for the iMac. The chip should be upgraded much before then, but I bet by that time they will have a few more upgrades for the iMac.
Mac Pro and Xserve have the Xeon (Woodcrest).
MacBook Pro, MacBook, and iMac will be upgraded to the Core 2 Duo (Merom) with iMac possibly being Conroe.
Mac Mini will probably keep the Core Duo (Yonah).
This sounds perfectly reasonable. Things are definately more interesting with the Intel chips because they are being rolled out so fast, unlike the PowerPC chips from Freescale/Motorola. It has only been about 6-7 months since the Core Duo was unveiled, now Core Duo 2 is here. Since Apple prides themselves on using advanced hardware, it only makes sense that they should upgrade the MacBook, MacBook Pro, and iMac to the Core 2 Duo (iMac=Conroe), and continue to upgrade to the best available chips Intel is offering at the time (aside from the 'extreme' editions).