When I was dealing in militaria I always used to advertised for medals and flying logbooks (as well as other items). Over the years I purchased many lovely groups of RAF medals, including DFC, DFM and AFC groups, a group to a Battle of Britain Air Gunner, and many more. However I hardly ever managed to obtain any logbooks, as they were deemed to be much more personal to the individual than the medals themselves. One lady was quite content to sell me her late husband's AFC group, but would not part with his logbook, which I fully understood. She did however lend it to me and it was fascinating. Around the time of the Normandy invasion he was the CO of a Mosquito squadron, and somewhere around D plus 3 he was shot down, but was lucky to parachute into friendly territory and was soon back on ops. The story behind that short logbook entry was that subsequent examination of camera footage revealed the fact that he had been shot down by one of his own squadron who had mistaken him for one of the Me110s they were "involved with", Hardly a career move on the part of the offending pilot!
Such is the sort of info that can make a logbook fascinating, and makes them hard to collect. I am always looking up things in my own rather slim logbook, and I know it will never be disposed of it until such time that it becomes the property of "the late TTN"
Chugalug - I wouldnt give the RAFM the time of day, let alone a logbook, and that goes for most museums. Unless it is exceptional it will disappear into a vault and never see the light of day again.