One thing that I always think UI wise, and it is perfectly demonstrable with a direct fremantle/harmattan comparison is use speed vs customizability. The N9 is faster to use than the N900, but you can never make it your own. You always see that same boring home screen, and the inability to pin apps in multitasking makes it impossible to 'glance and go', using a MS terminology. WP7 has built on this with the live tiles, and harmattan has the (mostly unused) live icons.

On the other hand the widgets on the N900 are good enough but as much as I tried to cram all my shortcuts in a home screen and use it as a launcher (ie never go to the menu) it never worked. It was always easier to go to the menu. I had installed a new app and that was not on my launcher screen, or my launcher was 3-4 swipes away in unknown direction. Having numbers on the home screens didn't help much as it required thinking rather than muscle-memory.

i think that the idea of fremantle that the switcher is more important than the launcher is great and we should try to build on that. How could we make the launcher better? One idea is to create a design spec to encourage applications to fill their screen with a large status message/icon when backgrounded (see cuteTube for harmattan). Another idea is to have ghosts of the mostly used applications after the running ones. And of course pinning, which would allow to run applications at startup, and have them always display info, like widgets.
Pinching could be used to resize any window thumbnail seperately.

Another thing that is awesomely useful is switching between the latest two applications without needing to go to the switcher first. This could be implemented with a gesture like e.g. Two finger swipe, or pinch from outside.

Now the desktop should remain because everybody loves it. See the maemo 5 screenshot thread. It gives you the ability to make your device your own, and build your user experience of preference. But it should incorporate the launcher functionality in a useful and easy way so that we can get rid of the third UI layer. I find myself clicking the top left button in frementle random number of times until I get to the screen I intended. That shouldn't be like that, the user should know where he is going next without thinking. Maybe the solution is to keep the flat harmattan home interface and add the ability to add up to $INT widget home screens, using a vertical arrangement for those, so that launcher/switcher still remain 1 swipe away.

Lastly I thought of the events screen useless, and I filled it up with rss etc. only so that it's not empty/unused. Now I am addicted to it, and I don't believe any number of widgets can replace it. Events should be aggregated and not be scattered around one tweet here, 3 rss entries there and two facebook comments elsewhere. I want to check what happened, not what happened in a specific network. There is the $APP for that.

These are my thoughts about the perfect phone UX. M*e*o OS's came close to that but there is always room for improvement.

Thanks for reading.