So we know you will be using it for photography. I have last year's version of the 24" Imac and love it. The additional screen size is worth buying it over the 20". Actually the specs on the current 24" Imac are outstanding performance wise. Even the new ones are worth the $1500 price tag IMO. If you can find one on the Apple refurb store, even better. Mine is also a refurb from Apple.
Those concerned about 2GB of RAM must have never used a Mac. The Mac OS does not eat RAM as much as the Windows platform does. You can operate Photoshop quite well with that amount of RAM. Just have to watch how many other apps you run concurrently. My Macbook Pro only has 2GB right now. It can run Photoshop and Lightroom together with no problems. For those that use both, Lightroom typically consumes much more RAM than Photoshop. I've seen it go up to 600MB on a regular basis.
One other thing...IWork '09 is $79 and opens all of your existing MS Office documents. Keynote absolutely blows Powerpoint out of the water.
All of this coming from a person who was in the IT field for many years as a Windows evangelist
