NOKIA should invest a lot more to strengthen the community (bugfixing or bring instead the new OS version officially to their devices when there is not enought manpower for the fixing of the old Bugs (we understand, double work)) and not to scare the userbase away by abandoning their bought devices only to earn more money by selling mostly identical hardware with improved software. This is not helpful!

Many N900 owners are at the moment very unsatisfied. Look at eBay! It's a great indicator. They are leaving the subsiding cruise liner. And this are not the new MeeGo customers. Not in the next few years...

My advice:
Make the Software independent. The people who wants improved Hardware (speed, camera, multitouch) has to buy a new device. And they will! The others got the fixes and Nokia can keep back new features only for new devices or sell it at the ovi store. (something similar does Apple with a lot of success)
The freaks purchase the new devices as soon as they arrive. The average acquire a new device every 2 years with a new contract. You can't attract them with a new device every 6 month only with bugfixing.

And I'm sure, then the userbase will grow strong. At the beginning mostly linux freaks... but this are the developers of tomorrow. With a pleased community the positiv sentiment will spread itself all over the internet (blogs, chats, icq, forum, wikis and at least the old print media) and Nokia could get a self marketing device for the mass market. (look again at Apple)

It's very Important: Implementing of missing features and Bug fixing has to be done. NOKIA needs customers which speaks after 2 years about it as "great device, the best I ever had". But when they say instead: "same software problems since the beginning, not well done" they wouldn't buy the next device. If Nokia gets rid of all unfinished feeling with the software during the device lifetime the users have at the end of this time a positive feeling. They majority has the problems in the beginning forgotten and go to buy the next, new Device. Otherwise I would say rather not.
It's very easy: Happy Customer are loyal Customer!