Being a Mac user who does (and by does I mean is starting to) do CAD, I'd suggest getting as much RAM as possible. And even though Apple doesn't endorse it....(http://www.amazon.com/Kingston-Techn.../dp/B001PS9UKW) works pretty well. Cheap. Easy install. I use it myself. Just be sure to get the right MHz for your compy.

*NOTE* The RAM in the link provided is for a standard Macbook, late 2010 model. It is the RAM I use, and that is the computer I use. Look into different types of RAM to fit your computer. PM me with your compy specs if you'd like and I can help find some good RAM for you.