I always think that a good user interface is an interface that try to make the user dev. an habit. I always use the holy grail of UI design Apple as a comparaison, the ways you use iTunes is the same ways your used it since the first 5 minutes you played with it, in that 5 minutes you have dev. an habit that is ingrained in your brain. The same way I can give my grandma an iPod and she'll figure out how to use it, I think that I can show a screen of gmail and everyone should be able to dev. an habit with it. So yeah I think they nailed it, damn I hate software that make it a point to make me go out of my way to use it.