2GB vs. 3GB Memory on 20'' Alu iMac

The jump from 1GB to 2GB will likely be far more noticable than 2GB to 3GB, (and going from 1 to 3 will be huge), but depending on what you use your computer for, it is hard to say. I use 2GB in my iMac, and it runs great. I do plan to upgrade to 3GB eventually, but that will only serve the purpose of future proofing my machine, rather than actually needing the extra power for high end apps.

I find it hard to recommend 2GB, since if you ever want to go 3GB in the future, you will basically have to throw one stick away. If you do any high end work, go the 3GB route. And if not, I say do it anyway.

You will probably notice very little difference when running every day tasks. More RAM might help if you are running Parallels or VMWare Fusion where you can allocate more RAM to the virtual machine.