IMHO in terms of usability the Maemo UI peaked at 3.x. There were some great ideas there like modifying the UI behaviour according to stylus vs finger input, work being done for resolution independence and so on. I understand there were limitations in the touchscreen hardware of the time, but if those could be worked out somehow instead of abandoning tablet-style usage patterns a lot of customers would be much happier.

It's not quite a deal breaker for me because the underlying system is much better and more open now, and I can tolerate a bad UI up to a point. But given a choice I would definitely go for the UI that optimises the use of screen real estate and the number of taps needed to do things rather than the one with the eye candy.

To say the least! The Maemo 5 UI looks appropriate for a phone, but also severely handicaped for anything larger like a tablet, MID or netbook. One size certainly does not fit all, and I suspect/hope we haven't seen the full story yet.