As always it depends on what you want to use it for.

I have both the Tamron 18-250 and the Nikkor 18-200. The Tamron is a little smaller and lighter. While it does lack the VR, we all seemed to survive pretty well without VR before it was introduced. I like the Tamron because it has some Macro ability which the Nikkor sorely lacks.

For a travel kit I think the D40 with the Tamron is a very good light-weight setup.

For $275 you got the Tamron for a steal. I paid a lot more for mine.