I can't add too much here that hasn't been said . . . I know when I first started I didn't want to post DNFs since I thought too many would make me look like a very bad geocacher . . . now as a cache owner and seeker I find DNF posts serve a very useful purpose and I'll post my DNFs even if I look foolish (well this look comes naturally to me.)
Logged DNFs to me don't mean a whole lot . . . however as a cache owner if I see a DNF or two on one of my caches I'll go to the cache and make sure it's there. In some cases the cache has been there, but it has been a trickier hide than I intended and so I've increased the difficulty level rating based on the DNFs.
In addition, when I see cachers log a DNF on one of my own caches (and I don't always catch every single one) I'll send the cacher an additional clue to help them out the next time they're in the area. Many other cachers do the same thing -- Northwoods Explorer for example and Hollora have done so . . . Hollora even gave me her cell phone number and came out to watch me search for her cache . . . and then discovered it was missing.
As a cache seeker I use previously logged DNFs as well . . . they give me an idea sometimes of how difficult a cache might be, if the cache might in fact be MIA if it's getting lots of DNFs, etc. If a cache has received a lot of DNFs and the hider has not put up a post noting that they have checked the cache and it is in fact still there sometimes I will by-pass that cache or not spend as much time looking for it.
So in summation . . . there is no shame in posting a DNF . . . Lord knows I've posted enough of them in the short time I've been geocaching.
"Courage is not the absence of fear, but the realization that there is something more important than fear."
"Death is only one of many ways to die."