RescueTime

Frequently Asked Questions | RescueTime: "RescueTime is a web-based time-management tool that allows you to easily understand how you spend your time. One of the coolest things about RescueTime is that there is NO DATA ENTRY. You install a doohicky on your computer and we magically track all of your time usage. For more info, check out the product tour.

Cool idea, but I always have a lot of different applications and sites open at any given time. How does RescueTime handle that ?
RescueTime doesn't really care which applications you have open, but rather pays attention to which applicaiton or site is currently 'in focus'. In other words, we're measuring what's what you are paying attention to, not what you have open."