I always appreciate a quality call, but I can't agree that native is a good proxy for good UI or even just for the principle of least surprise. We use so many different UIs nowadays. Various OSs, crazy web UIs, different phones, games, vim, etc. So for me, the question is not so much "is this app native?" but rather "am I a native of the app's UI? (or let's say naturalized :)". iCal doesn't feel native to me, even though I use a Mac. It feels awkward after having used Google Calendar for a while. (I would even say iCal has a horrible UI but that's another matter)
I happen to think that a good UI is not just a matter of getting used to it, although that's a big part of it. There are some things I do hundereds if not thousands of times a day, and I want them to be very fast, regardless of what is native. I want them to be the same in that particular app on all platforms I use. I don't want the keyboard shortcuts of gmail or vim to change depending on what machine I happen to use.
I happen to think that a good UI is not just a matter of getting used to it, although that's a big part of it. There are some things I do hundereds if not thousands of times a day, and I want them to be very fast, regardless of what is native. I want them to be the same in that particular app on all platforms I use. I don't want the keyboard shortcuts of gmail or vim to change depending on what machine I happen to use.