IMHO, the N900 is the only "mobile computer" for the GNU/Linux geek. This implies that you value freedom (tm) more than some features. I know I do.

If hackability and freedom aren't at the top of your list of priorities, you might as well go with a smartphone that "just works" (tm). and if that's the case, why not an android phone? Why either n97 or n900? I think some android phone might be somewhere in between those options in a lot of ways.

I really like the n900, but I'm really into the gnu/linux freedom thing.