Statistics about your overlays can be viewed and downloaded via stats.adnos.co.uk. However, if you require a deeper integration with with your existing system you can use the statistics api functions to obtain the data.
As well as offering a deeper integration, the statistics API offers more flexibility than the web interface. Exactly the same connection format is used as for the overlay functions, but as most people do not require this functionality access to the statistics functions is turned off by default.