Freelancer's Timer

I've had this idea for a little while to make what I'm calling the freelancer's timer. Basically, if you're engaged on a number of different projects throughout the day, then keeping track of billable hours is a pain. What I want is a simple switch or set of switches on my desk that correspond to a particular job I'm working on. When I turn one of them on, it updates a google spreadsheet where I can keep track of my time without having to input anything. Then at the end of the week I can graph or export my time sheet. This morning I made a little success in putting together an mvp of sorts: Electric Imp + Xively + Zapier -> Google spreadsheet. This is soon to become a collaboration with Jacob Dubail!