this is what I answered in a similar thread:
I have the 11,6" 128 gb, 2 gb ram, and have Logic 9.1.3 installed.
It's true that this setup is definitely not as fast and powerfull as my 3 year old iMac 24" (2,4 ghz, 4 gb ram asf.)
I ran a test with my new Macbook Air. stereo audio-file, 24 bit 44 khz, 1 minute long. For each track I put on a space designer reverb with its default preset, and put on a copy of the stereo-file on each track as well. The idea is to see how many tracks it's possible to open with a reverb added before Logic report a "too slow" message. The test has to run without any hickups the whole minute! The test with my iMac gave me around 60 tracks before it couldn't do any more tracks. The Macbook Air did 40 tracks before it stopped. Thats with a 1,4 ghz, 2 gb ram! I think thats processor-power enough for me for "on-the-road"-ideas and such. I would think twice if this was the only machine I had. Then I would have bought the MBP. But as a second machine, for a "on-the-road"purpose, I am more than satisfied!
b.r. andershoeg