By my calculations:
BRONZE 1 GH/s contract - now starts in Sept
At current difficulty, 1 GH/s earns 0.0322 BTC/day. But as you know difficulty has been skyrocketing. Previously, on avg every 2 weeks difficulty increased 10%, the past difficulty (and looks like coming difficulty) have increased on the order of 20-25%!
If this trend continues, by the time the Sept contract starts (say 10 wks from now, or 5 difficulty adjustments of 20% each), 1 GH/s will only bring 0.0131 BTC/day. A year of such mining (again assuming 20% increase in difficulty every 2 weeks) would only net 0.91 BTC total. Since a 1 GH/s contract costs $150 currently, the price of a BTC would have to be $167/BTC to *break even*, let alone earn back a profit.
Even the best PLATINUM contract at 10 GH/s starting in Sept would only earn back 9.21 BTC at the end of a year (with assumptions above). But in this case, BTC would only have to be $103/BTC to break even.
For comparison, a BFL 5 GH/s ASIC costs $274, so to get the same 10 GH/s power you would only need to spend $548 vs $950 for the Platinum contract.