Realistically, you should update your resume as often as your job and responsibilities change. That's how the Functional Resume serves. We also suggest you update your achievements list, which we call Milestone Mapping. It would also be worthwhile to do a reality check by performing CWW's BRC exercise and chart your skills in the Skills Charting exercise.
When you have to respond to the, "Tell me about yourself", or "What have you done lately.." questions, the need to pinpoint and clarify and how your resume works for you, won't be hard to do if you have these tools in place.
A good example and of significance, are special projects an individual handles throughout the year. These tasks need to be documented and harvested when the times comes to talk about what has been accomplished within a certain period of time and during performance evaluations.