I've owned the Macbook 12" for several months and I'm still not used to the keyboard. I'm a seasoned touch typist but there are keys I keep missing, and some keys that were initially not fully responding on all edges and required some continual tapping to get them fully working. the lower right corner of the spacebar has inconsistent response.
The result is that typing feels like a bit of a chore. I've tried positioning my hands in a more extended manner which seem to help a bit. Bottom line is that I prefer the older keyboard style and actually continue to miss my Macbook 11" even though the screen and resolution options are so much better with the Macbook 12".