Slip charts are an incredibly useful tool for managing projects. For those unfamiliar, here are two examples:

"A NASA Slip Chart":http://history.nasa.gov/SP-4210/images/gif/one_third/appf_1.gif

"A slip chart implemented in Excel":https://itxperiment.wordpress.com/2010/07/31/milestone-slip-chart/

In order to generate such a chart, any changes to milestone projected completion dates (milestone, date of change, new target) have to be stored. From that data, generating the visualization of slip is fairly straight forward.

Useful views would include full project enumeration (all milestones) and and statistical slip by higher level organization: project, sub issue, assignee, category, perhaps others.