My N900 (Made in Finland, an early one) was great. I would have used it still if it wasn't for the fact that after 3G disappeared it was useless. The battery could be replaced (as others have mentioned), so it was perfectly fine still. Mechanically it was as good as new as well.

As it was basically like Debian Linux inside I could do what I usually do - write hobby projects and run it on the N900. I had my minicomputer emulator running. Nice to see my old favourite minicomputer editor on my N900.