I think the limitations on the daily varation is a good idea, as it reduces volatility and reduces the sensitivity to "spikes" in the spot price.  The setup with 10% variation per clearing, and two clearings per day also seems like a reasonable compromise.  

However, I think the inability to place asks above the current maximum and bids below the current minimum is a bad thing, and should be allowed within an additional 10% or so.  I have three reasons.

1) If the spot market moves a lot, the price at ICBIT may hit the end of the allowed range.  In that case it becomes impossible to build an opposing side of the order book, and when the clearing happens the price moves rapidly as the relevant side of the order book is almost empty, except for a few ancient order left behind.

2) When the price thus moves suddenly, margin calls may happen.  But since the relevant side of the order book is empty, forces sell/buy cannot happen, and the "worst case scenario" will be invoked.  If we could pre-fill the relevant part of the order book before the clearing, we could act as counterparts to the forced liquidations.  The person being margin called would get a better price, and less people would see forced liquidations.  This is where it becomes important that there is still a limitation on the orders we can place, for example of another 10%.  That prevents me from placing buy orders at absurd prices like 0.1$ and hoping to profit unreasonably from someone to getting margin called.

3) Some of us are not able to sit in front of the browser 24/7, and may want to place orders relevant for the next trading session which are outside the range of the current one.

EDIT: Accidentally placing orders outside the trading range would be annoying, and it is nice that the interface prevents it.  So and additional step should be required to place such an order.  I suggest a check-box on the trading interface "Allow orders outside the trading range".  Even when checked, ask orders should only be allowed above the range, and buy orders below, and only within 10% as described above.