
The N900‘s Maemo 5 OS, shown below, doesn’t currently support portrait rotation:

The new info comes from the Maemo Summit, where the Fins also demonstrated an official Qt port specifically designed for Maemo 5. The Qt port (available now as a preview release) lets developers use a common framework to build apps for the N900, future Maemo 6 devices, in addition to Symbian and Windows Mobile.
[Nokia and UMPC Portal via Slashgear]