There is not a lot I can say about hiding caches. So far I have picked out a couple spots that ended up muggled before I even got permission to place the cache. . . but stay tuned (im still looking).
I can say what I have found that took the fun out of finding a cache. Not all of which relate directly to the placement of the cache.
10) Muddy Roads & long hikes to bla locations.
9) Religious pamphlets (Im the one who throws them away!)
8) Too many bugs (aka Geocacher blood donation location)
7) Nebulous puzzle answers (hmm. . . is that mauve or eggplant?)
6) Missing Travel bugs (some have been missing a very long time!)
5) No clear sky (last 10 logs say, "DNF! hard to get a signal here!")
4) No Tresspassing Signs!!!
3) Muggled Caches (too close to the beaten path?)
2) Coordinates off by more than 30'
1) Wet Logbooks (human error, containment failure and aqueous toys)
With that said, I wonder if there should be more "types" of caches or a kind of Finder Rating Score (FRS) to help people decide what to seek.
When close to home, I wouldn't mind searching for a cache that is nothing more than a place to drop a travel bug or log a find.
When traveling on vacation, I would like to be able to tell which caches are "worthy" of my time (estimated value $200 a day). One of the things I love most about Geocaching is finding hidden places that I probably never would have found otherwise.