Some astrobiologists believe the conditions for life are restricted to a galactic "habitable zone", marked roughly at the radius of the sun's orbit about the nucleus. They base their conclusions on chemical gradients in the galactic disk which are optimum about where we are. I personally don't believe this to be the case, since regardless of overall chemical gradients, there can always be pockets of isotopic enrichment scattered about randomly due to nucleogenesis in supernovae and dispersal from planetary nebulae.

There are other factors which supposedly make earth anthropically favored for life, such as the presence of a large moon (to stabilize our precession), and our position about our relatively massive primary which protects us from rotational resonance, or our magnetic field (protection from solar flares) and so on. But I personally don't think any of these is a deal-breaker. In my opinion, if liquid water is possible, life is probable. Life can always go underground, or under water. Still, we can't rule out that some of these factors might play a role of some sort.