MF Global customers fume as funds, trades frozen

Please note that customers of a failed brokerage firm get back all securities (such as stocks and bonds) that already are registered in their name or are in the process of being registered.  After this first step, the firm's remaining customer assets are then divided on a pro rata basis with funds shared in proportion to the size of claims. If sufficient funds are not available in the firm's customer accounts to satisfy claims within these limits, the reserve funds of SIPC are used to supplement the distribution, up to a ceiling of $500,000 per customer, including a maximum of $250,000 for cash claims.  Additional funds may be available to satisfy the remainder of customer claims after the cost of liquidating the brokerage firm is taken into account.

Attached is a good article on what to expect in the early days of the liquidation.