Here is a new paper on backdated options by Randall Heron and the guy who started it all, Erik Lie, What fraction of stock option grants to top executives have been backdated or manipulated?
We estimate that 18.9% of unscheduled, at-the-money option grants to top executives during the period 1996-2005 were backdated or otherwise manipulated. The fraction is 23.0% before the new two-day filing requirement took effect on August 29, 2002, and 10.0% afterward. For the minority of grants that are not filed within the required two-day window, the fraction backdated remains as high as 19.9%. We further find a higher frequency of backdating among tech firms, small firms, and firms with high stock price volatility. In addition, firms that use smaller (non-big-five) auditing firms are more likely to file their grants late. Finally, at the firm level, we estimate that 29.2% of firms manipulated grants to top executives at some point between 1996 and 2005.
Update: Erik Lie has information about backdating here.