In an absolute sense nearly any computer will work more efficiently with more RAM installed. The Mac OS X system can do more things quicker with the extra RAM. That said, if the computer is being used solely to run iTunes, then 1 Gb is more than sufficient for ripping and playback purposes. iTunes is not a RAM intensive program. But then again, I agree, RAM is cheap. If anyone can point to test(s) showing added RAM significantly decreasing rip times, please post.
One more time -- don't do anything else on the computer when ripping.
One more time -- don't do anything else on the computer when ripping.