There's lots of talk about nuclear platforms. I don't believe that's the case with the X-37B for a few reasons. We have better options elsewhere, the X-37B designs I've seen don't seem to fit this picture, and NASA/Boeing Space & Intelligence would not typically deal with nuclear weapon platforms.

I think it's clearly a reconnaissance (ISR) platform. Think Gorgon Stare [1] but for an even wider area. As an aside, Dryden has a long history of testing recon platforms.

Source: I used to work on this stuff (although not the X-37 program)

1. http://en.wikipedia.org/wiki/Gorgon_Stare