If you're not part of the soultion...
You're part of the precipitate!
At a recent housewarming party I went to, at some point in the party there were three games of Dominion being played at the same time in just one house.
Has anyone seen more? (Residential buildings only; hotels don't count.)
This probably doesn't count, but at a playtesting night at my house, we had five going on at once!
The most I've ever seen otherwise was three. (And I was not playing in any of those games nor had I provided any of the sets to be played that night)