Depending on your set-up, 2-4 people.
On one site, I'd say 6 is the max (2 in the car, 4 in a tent) ... I've never camped with just one site though, so that might be on the high side.
I say 4 comfortably. Take your tent down each morning for more space during the day.
8/20 Fucked Up - The Garage
8/22 NIN - Verizon Wireless Amphitheatre
8/23-8/24 FYF Fest - Exposition Park
8/30 Ty Segall - Echo
9/11 Swans - Roxy
9/30 King Crimson - Orpheum Theatre
10/29 Tycho - Ventura Theater
10/31 QOTSA - Forum
11/4 United Nations - Los Globos