Haha nice. I do basically the same thing except with a script.

    while true; do
        sleep 900
        zenity --entry --text="what u doin" >> done.txt
    done

Although now it's just a reminder that isn't logged.

    zenity --question --text "Are you working?"

It doesn't really mean "Are you goofing off" but rather "Are you doing what truly matters right now instead of refactoring code or responding to less-than-useful emails?"