Depends, what do you want to do with it?

Pros: It has T-Mobile 3G support and despite its age, it is still a very powerful little unit.

That said - I doubt we'll see a successor, I simply don't think Nokia will make "experiments" like this any more. It never sold much, but was very popular in the geek world for the reasons you mentioned.

If you like powerful phones that you can tinker with, you'll love the N900, and one day, it'll be a real collectors item.