Three weeks ago it launched on Steam, and in that short time it has sold approximately as many copies as it did in a year of being on XBLIG :) All hail the mighty Gaben! Still, I owe a lot to the XBLIG platform - every time I read about it seems like someone's saying something negative about it, but it actually put my game in front of a lot of players and gave me a "long tail" of sales even after I slipped off the new releases list. Many of the people that bought Survivalist on XBLIG went on to vote for it and write positive comments on the Steam Greenlight page, which I'm sure was a massive help getting onto Steam. Yet XBLIG itself is a completely open platform with no gatekeepers - you just have to pass peer review from other developers (which is more just a useful way to get feedback and testing rather than a barrier to entry).
So yeah, happy birthday Survivalist - and I hope XBLIG carries on long enough for me to be able to release some kind of a sequel on it.