Just search for "unused". Or use Google and try "Unused Whitney Permits". Here are the numbers for last year:Unused Whitney Permits for 2010
Most people who walk in and try for permits get the permits they want. For early September, mid-week, and Monday/Tuesday entry dates are best. But, there are many no-shows even on weekends.
The unused numbers are what is left after everyone walking in throughout the day and asking has been given a permit. Your chances are better if you arrive at the 11 a.m. time when numbers are drawn from a hat, and whoever gets the lowest number gets first choice.
Read box 6 of the Wilderness Permit Options topic (link on the left) for more info.