How do you track your time and expenses?

Hello freelance designers!
I'm interested in seeing how other track their time and expenses. I'm going to be building a system designed for freelance artists, designers, developers and writers. I'm planning on incorporating a "timeclock" which will be capable of project tracking as well as expense reporting. It will be smart enough to be able to bill different customers different rates or even to bill different rates for different projects for the same customer.

I also intend to incorporate "project templates" that could be used as a quote for new customers, saying "here's how I plan on spending my time" and show the expected billing for each portion of the project. I've heard that most designers are using a pencil/paper version of a timecard. this is usually inaccurate and does not provide any way of calculating what you should bill the customer or even a nicely formated invoice for your time.

Would anyone here be interested in such a system? What methods do you use now to track your time spent on project for all of your customers?