Journal your applications with Activity Audit and discover where your time goes.
Activity Audit creates a journal of the applications you use on your Mac. The journal acts as an audit trail, documenting which applications you use and how long you use each one. After just an hour, you will be amazed the information revealed by Activity Audit. After a day, you will gain new insights into your working pattern and how you spend your time on your Mac. Activity Audit works seamlessly with Mac OS X's iCal to bring you a calendar of your activity. Each time you open an application, a calendar event is created. The event is automatically extended as the application continues to run. When you quit the application, the event is completed. Activity Audit is quiet and unobtrusive. Once started, Activity Audit runs invisibly in the background. Designed to be started and left running, Activity Audit does not demand attention or alter your workflow. Start auditing, quit Activity Audit, and get on your with day.
I didn't find any method for accurately detailed front most app regardless of their brevity or obscurity, like screensavers or dialog windows. Try BackTrack.
Summary
If you want a carefree app for truly audit worthy billable hours, BackTrack works, but has a miserly user interface, that must be reworked in a database app that can handle the wealth of processes you never knew about, but has actually saved me in a actual $600,000 government audit and saved my bacon in many other priceless ways: a must have shareware for professional computing. I hope AA takes note because I welcome it's beautiful user interface.