Quote from gwac:
lol
Is this a limit up for the day or what? Does the index have a limit up also?
The overnight limits are about 5%. The RTH are about 10%.
So at open it "opens" back up.
Edit: I say "about" because the moves are calculated from the big spoos closing numbers.
FYI. things like SSO are still available.

Edit 3: For example SSO is trading at a premium to the ES. This is going to get interesting.