Join the club. I too guessed that any normal computer user reading the specs, with references to USB mass storage etc., would interpret them as you have. I got flamed by the big man. Apparently Nokia's customers are not supposed to be interested in host mode, even if the device is billed as a "computer", for Nokia's first time ever.

You need to read the earlier part of this thread and the discussion about what "support" means.

You should also read the long threads about host mode on earlier Maemo devices. It eventually turned out to be very easy to switch USB modes, once you got some basic facts that Nokia wasn't handing out. For a long time, Nokia's line was that you needed to have a Linux PC handy if you wanted to switch modes.

For the N900, as for the earlier devices, the default USB mode is to act as a peripheral device, connected to your PC for transferring files back and forth.

It is generally believed that the Maemo community will be able to figure out how to change modes on the new device, as it did for the earlier ones. Watch this forum for the next few months.