According to the Pat Choate report, "The USPTO has received 9060 requests for exparte reexaminations between the start of the process in July 1981 until Dec. 31, 2007. Of these:

-3945 were made by the patent owner (39%)

-5400 were made by third party (59%)

-165 were made by order of the commisioner of parnts (2%)"

"Patent owners file reexamination request primarily to test claims and to reinforce claim validity.

All the best,

Steve