Andrew Mason, CEO of Groupon, handles all of his own email. One of the most efficient emailers I've ever seen. He uses inbox zero with Omnifocus in a highly efficient manner. In the earlier days we used to try and come up with ways to make this more efficient by setting rules in Mail that filtered emails into different boxes based on how much time they sat. Most were his ideas. Last time I knew his process is it had been simplified to simply starring emails and relying heavily on Omnifocus. He would sometimes email you back in less than a minute. If you ask anyone that has worked with Andrew they'll note his thoughtful responses paired with his incredible response times.