I will pretty much always log a DNF if I feel like I gave it a concerted effort -- only reason not to log might be if there was muggles at GZ, or I was in too much of a rush to actually search. I do have some friends who don't log them -- I don't entirely understand their reasoning, I think having a blue dot on their map just annoys them. But I feel the same way, I'd rather have a record of what's been attempted vs. not. I'm impressed that HQ took such pains to look into people's behaviour, though! That was an interesting "study" to read