Nokia are pretty good at supporting their phones long term. Look at the Ovi store and still releases for older phones on Symbian. If Nokia forget about the n900 it will loose customers which in its situation (of missing the boat a few times of late), it won't forget about its loyal supporters. The majority of us on here a pleased with the N900 so we 'sell' it to friends and colleagues. Thats a better receommendation than any shop or review will provide.
I know Nokia have sold about 10 N900s just directly off the back of me. How many indirect sales I don't know.
maemo is new (to most). Ignoring its 5 custom base would be suicide.
Enjoy the n900. Lets face it who will keep it for much more than 12 months anyway before you want the latest bit of kit??