To be (un)fair, you can get used to a rock in your shoe as well. That doesn't mean you should.
Having to "get used" to a keyboard to return to your previous typing ability seems to be a contra-indicator of the new Macs having a good keyboard.
I'm also going to make what I think is a reasonable assumption and say that a vast majority of folks are going to carry their laptops around in bags. In which case, the 7 ounces saved (for reference sake, this is about the same weight as a 45 watt power brick, minus the extension cord) is nearly meaningless, and the half inch on each dimension will be completely meaningless.
On a side note, I think that a 13" monitor hits a sweet spot. It fits in a lot of bags, has just enough screen size to be productive without requiring an external monitor, and the performance difference between 13" and 15" computers is usually quite small (if it exists at all).
It's a cumulative process. My first Macbook was a white 13.3" polycarb core 2 duo. The new 15" MBP is a pound lighter, almost half as thick, and only half an inch deeper and an inch wider. Samsung has a 15" laptop that's under 3 pounds, making it very palatable even for people used to a 13"-er.
At what point along that evolution should Apple have stopped striving to get smaller?
Nicely put!