My dive log is a excell generated sheet in a binder. Untill i got my master card i was always asked for my log book when booking boats. The book is good for documenting your dives for courses that say you need 50 logged dives to get this certification. Granted that there is a point that count no longer has benifit. Anyone who would ask about a log book in not in that group. I keep notes about oocations, weighting, ect so i can use it later. Ie this dive needed 4 lb more weight than in local waters. weighting for my 3/2 sahorty, lavacore,, dry suit with 100g undergarment and 300g undergarment. 30 ft thermocline in june, dive shop is a rip off. ect. stamps are just gravey. For some of us ...... what weighting did i need when use to be 20lb lighter as i just lost weight. Logs are usefull. If you dive with me i would have your contact info so we could dive again. Every dive i try to do something that is training related like photography, bouyancy, deep ect. There are some agencies that will take you log info as proof demonstration. Ie i got my boat diving card because i passed the test and had logged several boat dives. The instructor des not have to witness your ability to jump and climb a ladder.