Adult-sized ball pit

[justben]

After a random chat with radiantbaby, vatavian, and rslatkin, I've become obsessed with the idea of an adult-sized ball pit, particularly with potential application as a bed. The big question in my mind, though, is one of volume. How much floor space would it need to take up to comfortably sleep -- or play -- two adults? Four? Six? And how deep would it need to be to support them? How does intended activity (sleep, ball-war, sex) affect the depth? And can a deep pool be used for shallow-pool activities like sleeping? Or would people just sink in uncomfortably?

Inquiring minds want to know.