We are choosing a new iMac, and don't know what processor to pick: do we just go for the 3.1MHz i5 or the i7, or...? And how much memory?
First off, everyone should buy a new Mac with 8GB of RAM (memory). You can also buy it after-market for a bit less, from http://macsales.com/ among others, but you want to get it pretty soon after purchasing the machine.
And with regard to screen size, if you do photos or videos, or just want to increase productivity by having a few windows visible simultaneously, certainly you want the 27" screen. Then it's just about the processor, and here's the scoop: For most operations, you wouldn't notice a difference between the i5 and the i7. But once you start in on iPhoto or iMovie, the i7 will be noticeably faster. And the faster machine will have a bit longer lifetime, accepting new upgrades to OS X farther into the future. I say "a bit," because for some people, the extra cost won't be justified by that extra longevity. If you went for the i5, go for the speedier version (e.g. 3.1 MHz is faster than 2.7). Thanks for inspiring this post!