I have my dive buddy or another along on the dive sign off on that dive. I log every dive, and have since I was certified 14 years ago. I do not understand those who say "I don't log dives" or "no one has ever looked at my log book." First of all, I look at my dive log all the time. I look at it to review information I record about weighting and air consumption in various conditions and wearing a variety of equipment. I look at it before returning to an area where I have dove in the past to note any particularly good sites or boring sites, hazards, interesting observations, and so on. If you are an adventurous diver and want to go on some particularly challenging dives with operators in some locations, they will ask to see that you have a certain number of logged dives. (Hammerhead dive off Molokai, for example). Some will want documentation of your most recent dive within a given period, or may require a scuba review. It 's true. I suppose you could lie, but why? To get to do a dive beyond your competence? That is not a very good idea. I have a stamp and so does my wife. People we dive with invite us to "stamp" their book- it makes the page more colorful. I also collect contact information in my log book from local divers we have met at far away sites, so I can call them if I need someone to dive with. Finally, if you are a dive professional, someone has looked at your dive book at least once, and may want to look at it more than once if a liability issue arises in the future. If you are looking for a job in the dive industry, documented experience is always a plus. To each his own, however. I for one chose to keep a dive log for my own benefit and entertainment, and to document for others my experience level if needed. My wife does the same. I encourage others to do the same.
DivemasterDennis