Hurrian's "query" is very good way to check, if you may enjoy N900. I could propose another one, though:

Do you want to have full-fledged mobile computer (first) powered by GNU/Linux in your pocket, with phone functionality (second, always)?

N900 is exactly that - mobile computer, which all things related to it (enormous capabilities, but just like with any linux-powered computer, you must get your hand dirty, from time to time). This can't be said about N9, upcoming Ubuntu phone (probably), or any other device, except for very niche (and much more hardware-limited) openmoko's.

So the thing is, what you really want. If you want smartphone (so you can remain dumb ), you won't be satisfied. If you're, hoever - at least in part - geek, look no more.

/Estel