If I got my three tasks done, it was a productive day and anything else I did was gravy. If I didn't, I forced myself to look back at what I spent my time on that day. The three-task system helped me get focused to avoid "fake work" like meetings, emails, etc.
I eventually coded it up into a simple tool for myself that I still use every day. I haven't focused on marketing so I'm honestly the only user, but I'd love if the folks here could check it out and tell me what you think - http://three.do