The problem is, the N900 is as much a computer as ANY device running an OS on an ARM CPU. Think about the set of devices that encompasses. The N900 distinguishes itself from them for better or worse by its OS (generally better except for available apps), its CPU speed (dropping in the polls as faster chips hit the market), and its RAM (still #1, I think).

But, I would argue, it is not an UMPC - an Ultra Mobile Personal Computer - competitor. Right now, I would describe the dividing line between a real, general purpose computer and a really smart smartphone in terms of a task: create a presentation in OpenOffice and show it to a meeting in at least 800x600 resolution on a projector using only the device, a cable, and a standard projector.

The combination of power (to run OpenOffice for content creation productively, not as an experiment), screen real estate and pointer resolution (to deal with manipulating graphics), and external display support (to run a projector or external monitor) is what makes the N900 less than a real computer in your pocket. A year from now, all bets are off thanks to Moore.