I have the N800, N810 and now an N900. The N810 I have loaned to my sister to use for Skype, the N800 is my bedside alarm clock/internet radio and the N900 is my main mobile. For users who were like me and perfectly content with the N810 apart from the fact that it lacked a phone application the N900 is basically the holy grail device.

Maemo 5 on the N900 is simply a much more polished experience than Diablo. The screen size reduction sucks but the addition of a usable point and shoot camera and the powerful processor really make up for that. Apart from screen size I really do miss the hardware full screen toggle like another poster mentioned.

BTW I don't think you will find too many prior tablet users complaining about the N900 much, all the noise is nearly all newer users who did not know what they were getting into with maemo and Nokia.