Here’s an excellent unboxing and hardware review of the Nokia N900. Normally I’m against unboxing videos, but this is Nokia’s press-only hacker-box, so I will make an exception.
If it wasn’t so damn expensive (it’s over $500 without a contract, and that’s the only way you can buy it in the US right now), I would give up my iPhone for it.
Maemo is a very good OS. I would say that at this point, it’s somewhere between the iPhone OS and Android. You get the open source and hackery elements of Android, but with the same kind of polish and intuitiveness that you find on the iPhone. Maemo also has an app selection that is nearly as large or potentially larger than what is available for the iPhone or Android. Maemo is linux, it’s not very difficult to port applications for it. You can basically install any Debian ARM package on it.
It probably functions better as a phone than the iPhone does as well.