1. Even one DNF puts up red flags in the minds of alot of cachers. Even if only subconsciously. Yes, it technically means only one person was unsuccessful, but the negative perception will be there.
2. Saying "that's their problem" is inconsiderate. If something I do in this game affects how other people play it (especially negatively), then it is my problem too.
3. Not logging a DNF doesn't mean that it is unacknowledged; in fact, in my mind, not logging a DNF means I am resolved to come back and try again.
4. You definitely shouldn't use the NM log unless you KNOW there is something wrong with the cache. (ex. You find the cache is cracked and filled with water, or the log book is damp, or needs replacing). As a cache owner, nothing is more frustrating than a NM log on a cache that is perfectly fine.
5. This is how we handle DNFs in Manitoba, and I am glad for it. And I would hazard a guess that most Manitoban cachers like this modus operandi as well. Other regions may have other systems that work perfectly fine. I wanted to give a different perspective on it.
Thanks for all the cheery, respectful replies.