This excerpt taken from the ALL DEF 14A filed Apr 2, 2008.
Each RSU represents our promise to transfer one fully vested share of stock in the future if and when the restrictions expire (when the RSU "vests"). RSUs are linked to stockholder value and are a tool for retaining executive talent.
Unlike options, RSUs retain some value even if the price of the stock declines. Because RSUs are based on and payable in stock, they serve to reinforce the alignment of interests of our executives and our stockholders. In addition, because RSUs have a real, current value that is forfeited, except in some circumstances, if an executive terminates employment before the RSUs vest, they provide a significant retention incentive. Under the terms of the RSU awards, the executives have only the rights of general unsecured creditors of Allstate and no rights as stockholders until delivery of the underlying shares.