Just read this over at the Verge...
Shortly before publication, Spelunky entered Microsoft's final certification process. Should it be approved, it could see release as soon as this summer, though no official date has been scheduled.
The freeware version of this game on PC is probably my favorite indie game of all time. Hopefully everything that was good with the original version carries over and is better on this release.
Also surprise Summer of Arcade Release!?!?!