MCC is correct, there's no such "optimization" for a specific processor. They simply use the processor in the family (whether it's the core 2 duo in the 13 inch or the core i5 in the larger ones) that meets a price/performance ratio that will sell. In the future, prices will drop on processors, invariably. While it's being mentioned, the slight processor speed increase, and the associated cost, of a Macbook upgrade is not worth it. For example, the 15 inch has a $400 upgrade to go from a 2.4 ghz/320gb hdd to 2.66 ghz/500gb hdd. The speed difference means that, if you were to run a two hour long processor-intensive process, you would save about 6 minutes with the faster processor. In a year or so though, there will be a much faster/ more efficient processor that simply plugs into the same socket. Take that $400 and buy yourself something nice.
Upgrading to a 500gb hard drive is simple in the future, and user-replaced hard drives don't void the warranty for opening up the computer. In my white plastic Macbook, I waited until I had actually started using a significant amount of hard drive space, and then bought myself a 7200 rpm drive. I bought an external hard drive with firewire and usb, and used the firewire to connect the old hard drive, installed in the enclosure. The new hard drive will see it as a mac and literally upgrade everything to exactly how you had it. It will be identical to what you had been using, just more space. Then format the old hard drive, and use it for whatever (I formatted it with FAT, so that I can transfer files to friends with PCs, plus I can put movies on the hard drive that the xbox can read).
Regardless, this is threadjacking to the OP. Get a Mac if you want, but if it's your only computer, I'd recommend a solid PC laptop that is more futureproof. Then again, Macs hold their value enough to sell to the Apple-loving idiots that still pay 70% of a used products value, 3 years after it's released.