best practices for keeping / using library circ data

I'm looking for best practices for keeping and using library usage data--real life examples of libraries gathering and using things like circulation data or e-resource traffic statistics to inform service and strategy decisions while safeguarding patron privacy. 

I'm less interested in operational logging for security / authorization purposes, and more interested in things like gathering data to make recommendations (people who checked this out also checked this out...), collection management / licensing / deaccessioning decisions, or overall library / collection usage reporting--especially if the data are tracked and used at more than a gross level (i.e., faculty v. graduate v. undergrad usage). 

What usage data do you keep that may be correlated to patron identity?
How do you use it? 
What do you do to anonymize / aggregate / cleanse / protect patron privacy? 

Does anyone have an approach that they regard as state of the art? Or pointers to previous work done in this space? 

Thanks in advance, 

- Tom