I think keeping your log book as a way to track your progress is a great idea. Depths, conditions, air consumption, weight... as well as the memories...... Now days with so many people paying for the next level of certification I would much rather know that my instructor had experience in all conditions.. If I was to employ an instuctor, regardless of the amount of dives they had supposedly done I would want to check this against their log book. Say a person has numerous dives in a tropical location? This doesn't mean they will have any experience in bad visibility, cold water etc etc. Either way it's a good record for both yourself, your buddies and dive operators that you may choose to dive with recreationally or professionally now and in the future.