We needed a field to show total hours tracked to Sick time and Vacation time Projects for a Resource. This is easy to do with reports, but we needed fields to be populated so we could use them in a formula to calculate PTO balances.
Create a rollup from the Timecard Header object to a field on the Contact object called "Sick Hours Tracked" and "Vacation Hours Tracked." Send along the sum of the Total Hours field on the Timecard for all Timecards that are for the Sick Time Project, and the Vacation Time Project, respectively.