I'd just like to point out a few things since people seem to be confused by the naming. There is no such thing as a Montevina CPU as well as there was no such thing as a Santa Rosa CPU. These are platforms that are used by PCs. Why do you think PCs have Intel Centrino Duo (codename: Santa Rosa) sticker on them, when the Macs have only Intel Core 2 Duo?
That's because the platforms are for PCs and Macs don't use those platforms, which are PC-specific. A platform includes all the following things: Intel PRO/Wireless network adapter, Intel mobile processor, Intel mobile chipset (southbridge and northbridge).
During the Santa Rosa period, there were two CPU upgrades, the original Merom (later updated with what you people refer to as Santa Rosa CPUs, which is incorrect since all they were were updated Merom chips) and Penryn.
During the new Montevina period, the introductory CPU is updated Penryn chips. So, NO these new iMacs do NOT have Montevina chips (because there's NO such thing), they are updated Penryn chips.
Source:
http://en.wikipedia.org/wiki/Centrino#Montevina_platform_.282008.29
for the non-believers (and I will recopy this post into every thread where people ask if the new MBP will have Montevina chips and I can tell you that they won't, they'll have updated Penryn chips MEANT for the PC Montevina platform).