At near-on midnight on Saturday, there were 150-200 people sitting in a 70m stretch of the main public park area here in Brisbane CBD (Southbank). During Sunday when I walked through, that was closer to 250-300. This is purely because there's 3 or 4 points of interest in close proximity so people congregate there to interact with it. It's truly a sight to behold.
This game has captured the imagination of non-gamers better than anything I can think of in recent history. It's nearing WoW / CoD levels of ubiquity.