Is there an app that allows me to monitor time spent using an application? Is there a tool that allows you to monitor the amount of time spent actively interacting with an application? This would be useful for development work to get an idea of just how long projects take.

EDIT:

I've been using RescueTime as it tracks apps, catagorises them based on productivity levels, and also looks at web pages visited.
Timing helps in tracking time spent in applications (and their windows) as well. It's similar to Time Sink but seems to provide more grouping and reporting options.