Its interesting to read all of the responses here I have just slogged through the entire thread. It seems that if Nokia had maintained a 4 inch screen there would be a lot less complaining, but something makes me think that is wishful thinking. Anyway here is my two cents.

Users on this forum are of a very specific type, this being very picky, very savvy, intelligent developers and gadget hounds.
In my specific case I am not very intelligent, I'm slightly savvy, I am not a developer but I am a gadget hound therefore I can find a small place here but 90% of the time I do feel that discussions are taking place over my head as I don't like to do anything from command line. Contrast this with my real world where I am considered one of the most 'techy people' in my immediate circle, if anyone has a question about anything tech related they come to me any advice about phones, computers, websites etc they come to me.
NONE of my friends have an N810 or N800 or have even really heard about it apart from one person and him only because he is one of the actors in the N810 promo video found on the device however nearly 40-50% of them have iPhones.

When they come over to my house I am always doing something neat with my tablet streaming music, or controlling my PS3 or my computer in the other room etc, they all always ask if its a phone, and when I tell them it is more like a minilaptop they play around with it for a minute or two and then finish nearly uniformly with the statement, "Nice toy, it would be great if it was a phone".

Ladies and gentlemen this is who Nokia are targeting with the N900. You and me had many years of great utility out of 770's and N8x0's and have created a useful position for our tablets in our lives. For the majority of the market IMHO I believe there is no position for a small handheld device like this that can't be replaced by a recent smartphone or a 10 inch netbook. Now with a smaller more pocketable size (yes 3.5 inches is more pocketable) and 3G data and voice all of these people can consider using this software instead of Android, WinMo or Mobile OSX, which I vastly prefer because for the most part you can stick desktop applications with hildonizing directly onto the device. I love that I have Transmission running and OpenOffice and GIMP its really amazing to have these experiences at a mobile level. This will in turn grow the community and perhaps spur even more application porting from the likes of people who work on Jailbroken iphones etc.

I have a 5800 XM which I have been using for the past few weeks leaving my N810 at home and have really loved having my twitter client running, and access to a nice large screen (versus the standard 2.4 inch mobile screens). However when I get home I switch immediately to the n810 because I love the maemo environment and all my applications on it. If this rumored N900 is true then I am in heaven because I can finally ditch the limitations of mobile phone OS's and have the best OS always in my pocket at all times.
I also don't envision stopping using my N810 or N800 either, Mer will keep these devices current for a while to come.