What is the weekly return rate in BTC of one asicminer share?
That's a matter of great thought. It depends on the amount of hashes asicminer brings to the network (and when) and when/if bfl delivers.
Essentially, asicminer will take their weekly income less expenses and divide it amount 400,000 shares. The going market price is .72 btc per share. Assuming market forces at work... this means the .72 is a discount on the future value of the shares.