Chris, what do you mean by "the UI to rotate"?
It's pretty generic and I think that's the source of confusion.

Maemo 5 DOES handle rotation. The accelerometer does tell you that.
Not sure if Maemo emits a D-Bus event for that.

Any application can detect it and rotate if they wish so.
Xournal will probably do it.

The issue here is that (a part from the Phone application) no other stock application does rotate.
It's just that the code to rotate (i.e. to generate the NEW UI in portrait mode) is not done.

You must understand that the N900 is not a phone that comes with Internet as we know it.
It's Internet with a Phone capability added. Even more specific, it's an Internet Tablet that can make GSM calls.
Internet Tablets always had the Call feature, now they can do it over GSM as well.

The landscape mode is a direct heritage of this past. And it is MEANT to be used as such.

Indeed, I didn't want the Phone. It was fine to have a slot for a DATA only SIM card for me but still having a nice 4" screen.

Hopefully I am not missing the point and I am not saying what's already been said.

Anidel