I dont know about you, but I regularly use my N810 (of not the N800 maybe, but still same software) as

1) Call my home using Skype and Gizmo (I use Gizmo where Video is required and for Desktop to dektop), Skype for all other international calls

2) Use it as a excellent Podcast player and Audio player

3) Use it to connect wirelessly to the internet and read my blogs on the train - with a fast 3G connection over bluetooth

4) Wirelessly update and install apps on my N810 when ta home over Wifi or over Bluetooth at office

5) Use it as my contact manager and Calendar app - which also shows me my shared calendars on Google Calendar

6) I use it to jot down notes regularly while I am out and about.

7) Lastly also use it to watch my encoded movies while on plane trips (instead of watching the crappy fare).

8) Keep a tab on 5 day weather forecast while I am commuting from place to place or each regions weather conditions (OMweather).

9) Check emails and write and reply to my personal emails from the device - from anywhere using Wifi where available and BT PAN over my 3G connection thru phone.

10) sometimes as a last resort solution when I am mobile, I SSH into my servers and run or start/stop jobs which I am looking after.

Now that is all just usages which I do every day.

We can talk about the less often used features ... later when you stop smoking the crap that you are smoking when you talk about "dubious usefulness".