I love my N800, and use it everyday. the only time I put it down is when it needs charging, and when I'm asleep.
Sure it may do things less well than specialist devices with a limited function set, but it does a lot more. It is the IT equivilent of a swiss army knife
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I have a standalone satnav, mp3 player, mp4 player, but the Nokia does that, and does vnc, xterm, video podcast, rss, office apps, internet, video etc., and in one fairly small pocketable box, I cannot fit my garmin, and my Archos in one pocket together, and that is only 2 apps.

A laptop, or netbook, will do the others, but again will not fit in a pocket. If I could get a data-only bluetooth-accessible 3G modem and mobile deal, I could scrap my mobile phone.

IPods and Iphones are nicely designed etc, but you cannot upgrade or swap out the storage. You cannot just drag and drop videos and mp3s to the device, you need to have an application installed on the PC ( or you did until recently)

I have an S60 phone, and the only app I really use on it is sports tracker, just about the rest of the time, my tablet is also there, and does it better on a bigger easier to use screen.