Are we living in a giant cosmic void?

The paper "Living in a Void: Testing the Copernican Principle with Distant Supernovae" by Timothy Clifton, Pedro G. Ferreira, Kate Land, argues that if we are living in a giant void - that is, if our cosmic neighbourhood is significantly less dense than other parts of the universe, then that could account for the fact that the universe's expansion appears to be accelerating.
As the New Scienist notes, "In fact, if the void were big enough - roughly the size of our observable universe - it might account for the supernovae observations that imply acceleration, and do away with the need for dark energy."

Source: http://lanl.arxiv.org/abs/0807.1443