While it has yet to reach its full potential, the Nokia N900 is a powerful mobile device with excellent browsing capabilities and vast customization options. However, its unintuitive interface and other limitations make this a smartphone for tech enthusiasts and early adopters only.
As a second, dedicated browsing device or a geeky weekend hobby, though...the N900 is a very compelling device indeed, as long as you remember one simple rule: it's a computer with a phone, not a phone that can compute.
This is a great phone/mobile computer if you're into this kind of thing. If you wanted a Nokia Internet Tablet but were put off because of their size and the fact you need a mobile as well, this is the answer you've been looking for.