The Government have published two annual reports that contain statistical information about how many requests have been received by monitored bodies (including central Government Departments) and how many have been refused.
These reports can be found at the following address:
http://www.foi.gov.uk/reference/statisticsAndReports.htm
Data are currently being collated across monitored bodies in order to produce the 2007 Annual report and Q4 Monitoring report, however, Q1-Q3 Monitoring reports of 2007 can be found at the following address:
http://www.justice.gov.uk/publications/freedomofinformationquarterly.htm