As a newcomer to geocaching, I don't see why someone even considers logging a find that they didn't actually find. Out of 7 searches I've made so far, 2 were not found, and I didn't have a problem saying that, even though I KNOW I was "right there". I would think it's important to note when a cache is "not found" as it could be missing and the owner needs to know.
That's my opinion, and I think everyone it entitled to it. (My opinion, that is!)
sbellis