The lack of portrait support on the N900 has been highlighted as one of its major weakness, therefore it was no surprise that it topped the Nokia Conversations poll for the most wanted feature. Nokia understands and is at work (portrait mode for the web browser coming by Christmas) but meanwhile it looks as if the Maemo Community will also come through.
Thomas has just published a video of an application called Panucci, which is under development. Panucci is a media player for the N900 that completely supports both the portrait and the landscape mode. You can switch between modes by simply turning the device.
The above video is based on the first working version of the application and he promises it will be in extras-testing soon.