The Green Lake library had that Swoon on hand, so I've examined it carefully for town-square orgies. It is not a precise match (widespread licentiousness at the homecoming dance is probably the closest bit, though certain post-hayride group events seem to have gone a bit farther) but given the sheer volume of sexytimes I can see why a person would remember it as the town square. The writing made me a little crazy -- is it Twilight that's made people intersperse purple-prose bombs with their hippest slang? -- but I liked the ending.