I recently bought a professional line Nikon DX lens (17-55mm f 2.8) and, just because I wanted one, I bought an external flash with it (Nikon SB-700). The only reason I bought the flash was because all my friends have at least one, so I wanted one, too! I quickly realized, though, that this was a good call. Because the Nikon 17-55's enclosure is so huge, using the pop-up flash casts a really weird arched shadow on all of the photos, and when you use the supplied lens hood (HB-31), the shadow is bigger!
Check out the demo photos I took and annotated.