Facelesstech made his own Raspberry pi shutdown button and wrote a post on his blog detailing its assembly:
One thing I learn from my last shut down button was that the raspberry pi has internal pull up resistors so I didn’t need a 10k and a 1k pull up resistor on this design. This would save me a lot of space and pins on the new revision.
The reason I have decided to use these pins is that it doesn’t block any important pins you might be wanting to use during prototype of your project. All the other shut down buttons cover over the pins at the top of the header which include the SPI pins and most of the power pins. I have to admit mine doesn’t seam to be a bit more difficult to place in the correct place but I think that its a small price to pay for not having the important pins covered.
More details at Facelesstech blog.