How many votes does a game need to get selected?
It's going to change during the first few days/weeks since we don't know what kind of traffic to expect. Part of the drive for this system is the need for customers to help us prioritize which games they want to see made available on Steam. So the specific number of votes doesn't matter as much as relative interest in a game compared with other games in Steam Greenlight.
We're going to be reaching out to developers as we see their games getting traction regardless of whether they have achieved a specific number of votes or are sitting 1st or 2nd place at any given time. We are most interested in finding the games that people want, not requiring them to always hit a specific number of votes.