A few years ago Mike Treder, Director of the Institute for Ethics and Emerging Technologies, laid out three propositions for dealing with Fermi's Paradox; after dismissing the first two (the second one maybe a bit too easily), he expounded on the third, which says that there have been advanced alien civilizations, but that they've always hit a "cosmic roadblock" that either prevented them from traveling too far from their origins or otherwise destroyed them.
Continuing with that logic he went on to say this about us:
Whatever civilizations have come before us have been unable to surpass the cosmic roadblock. They are either destroyed or limited in such a way that absolutely precludes their expansion into the visible universe. If that is indeed the case — and it would seem to be the most logical explanation for Fermi's Paradox — then there is some immutable law that we too must expect to encounter at some point. We are, effectively, sentenced to death or, at best, life in the prison of a near-space bubble.
This latest article (from March 2010) has Mike following up on reactions to that earlier piece, including his thoughts on many of the alternative propositions submitted by readers. Ultimately Mike ends up where he left off three years ago: "All in all, it seems clear to me -- irrefutably logical -- that some sort of cosmic roadblock, as yet unidentified, must exist. Either that or we are in a simulation."
(For those interested in this sort of thing, you'll definitely want to check out the comments.)