Furthermore, when the multiple cores aren't being used efficiently, this chip can boost its clock speed all the way up to 3.46 GHz to compensate.
I presume OS X will be making heavy use of Intel's Enhanced Speedstep Technology to keep power usage down, and to keep the iMac quiet. While it's possible the new iMac will be significantly louder at full tilt, I think most people will be fine with that compromise, as long as the machine remains quiet with surfing, basic business applications, and email.
Another interesting feature is the size and shape. The previous 24" iMac had a height of 20.5". The height is actually slightly smaller on the new iMac, at 20.4", which means the overall height isn't any taller than the previous 24" iMac. While this is still tall, the centre of the screen has now been shifted downwards, as the size of the "chin" at the bottom of the iMac has been decreased. I was thinking that with a larger screen I might have to resort to a VESA mount to bring the screen lower for better ergonomics, but with this change it may not be absolutely necessary. The widescreen format doesn't hurt either, as more pixels are distributed sideways, at the expense of vertical resolution. If I do decide to lower it more, there still the option of the VESA mount available with the 27". It's not available with the 21.5" iMac, but it's much less needed for that unit.
The most welcome upgrade to most people however is the addition of two more memory slots in the new iMac. FINALLY, Apple has included 4 memory slots in the iMac. 8 GB of RAM is now relatively inexpensive using 2 GB RAM modules, and the hardcore geeks can upgrade the thing all the way up to 16 GB. The iMac still uses SO-DIMMs which are usually reserved for laptops, but that's fine by me.
Apple almost hit one out of the park with this upgrade. I immediately put my order in:
27" Quad-core iMac
2.8 GHz Core i7, with Turbo Boost up to 3.46 GHz.
4 GB DDR3 RAM (to be upgraded to 8 GB)
ATI Radeon HD 4850 GPU with 512 MB RAM
2 TB hard drive
I had decided to forego Apple Bluetooth devices, since my experience with them has not been pleasant. I said it'd take "some serious marketing" for me to get even the multi-touch mouse. I did forego the Bluetooth keyboard, and ordered the wired keyboard with numeric keypad, but caved on the Magic Mouse. It's new and seems interesting, but most importantly it comes free with the iMac. Since I already have RF mice and wired mice I can use if I don't like it, I figured it can't hurt to give it a shot, but the option of a wired Magic Mouse would have been nice.
There is one big downer about the new iMac though. While it has a Firewire 800 port, it only has one of them. This represents a loss of the Firewire 400 port from my three year-old iMac Core 2 Duo, although it is not unexpected since recent iMacs only had the Firewire 800 port too. This wouldn't be a big issue if Firewire 800 hubs were common, but they aren't. I currently use a Firewire 800 Compact Flash reader. With about 15 GB of files on a card, my USB 2 reader takes forever, and OS X tells me it would take about 10 minutes with Firewire 400. With Firewire 800 it's only about two-thirds that time, shaving off several minutes. Either I downgrade the port with a Firewire 400 hub to Firewire 400 only and deal with the slower speeds, or else I scrap my Firewire 400 drives for USB 2, and use the lone Firewire 800 port with my Compact Flash reader at full speed. Neither is an ideal solution.
[Updated 2009-10-23]
Although I could not find a FW800 hub locally, I was able to find a Kramer VS-FW30 3-port Firewire 800 hub available at a respectable out-of-country online vendor, so I promptly ordered it. I'll be sure to post back once I've had a chance to give it a whirl.