According to the Australian section of the official Xbox website, we may be finding ourselves incinerating aliens and threatening suspicious bartenders before the year reaches its midpoint. A product blurb dedicated to BioWare's galaxy-spanning sci-fi RPG, Mass Effect, currently lists a release date of 18 May 2007, a bit more specific than the "2007" placeholder appended to the likes of Forza Motorsport 2 (which is set to arrive sometime in May).
It's worth noting that Microsoft has yet to officially announce a release date for Mass Effect. At the time of writing, they had not yet responded to our request for comment.
Update: As expected, the reply doesn't deny or confirm the accuracy of the date, but notes that, "Microsoft has not yet announced a release date and the one listed on Xbox.com should not be treated as such an announcement." The information will likely disappear from the page soon.