It isn't all about the GHz buddy. First off, I don't really care for the plastic MacBook, but it is a very popular laptop on my university campus.
Back to performance. I have a 2.8GHz Core2Duo 4GB RAM 17" uMBP with 1920x1200 LED display. The screen itself is superior to any other 17" screen I have ever seen in my entire life. Being as I spend countless hours a day looking at the thing, a high quality screen is incredibly important to me.
For speed, 2.8GHz is just fine. I don't do processor intensive tasks so having a 3.2GHz processor would make no darn difference to me. I rarely do gaming either, so the 512MB video card works perfectly for my needs. And the 8 hour battery is perfect, and my friends with PC's and 2 hour batteries are very envious of the fact that I never have my charger with me, because I don't need it. And they are jealous of my backlit keyboard as well.
So reduced performance? I don't think so. I challenge the typical customer to tell me the difference their 400MHz faster processor makes. Some customers see that they can get a faster processor by not getting a Mac and say "ZOMG I NEED THAT SPEED", when in reality they don't. I weighed the specs of the internal hardware with the incredible design, screen, keyboard, trackpad, and RESALE VALUE of a Mac, and I am glad I picked Mac.
So when a PC user tries to sell their uber-laptop 2 years after getting it and only can get a small fraction of what they paid, I will be laughing to the bank having only lost a few hundred dollars selling mine after two years.