Saluting: Have you ever encountered an officer that did not salute you back, although he/she recognized your salute?

Yes, but only one. A WO2.

In my squadron most Os didn't like to be saluted,but we felt they deserved the respect. We would make sure we went out of our way to show them that respect they deserved. All but the cool ones we let them slide!

Yes. I was brand new and I saluted a Colonel. He looked at me an kept walking. I did the smart thing, I kept walking also! I never forgot how that felt, so I it a point to greet and return all salutes.

I've seen it happen to both myself while a PFC and an NCO in my Platoon. While standing in front of our building, a 1LT approached the doors and we Saluted while with the units motto. The 1LT looked at us and continued to walk past. As I continued to stand their puzzled as a PFC, my NCO approached the 1LT while at the position of attention, and the 1LT isn't that he didn't fell like saluting and told my NCO to move out. My NCO then reported it to our Platoon Sergeant and PL. I heard it happening all around post with other Soldiers but never to me after this experience a few years back.

I don't think I ever had an Officer not return my salute. However, in 2004 when I was just a lowly PFC in Korea, I actually had a MAJ walk a large box AROUND ME in order to avoid saluting me back! I was crossing a large parking lot on my way to a building with some paperwork in my hand, when I saw someone in uniform coming towards me. Since I couldn't see their rank yet, I went ahead and shifted everything to my left arm just in case, and as we got closer I saw his MAJ rank. I guess by then he saw I was enlisted, b/c he made a stank face and then made a box AROUND ME, as if he were doing land nav and going around an object! Being the green young Soldier I was, I thought perhaps maybe I had a large zit or something about my appearance had offended him, so as soon as I got indoors I quickly checked my reflection in the mirror -- nope. Turns out he just didn't feel like saluting back. Smh lol.

This was back in AIT, we're in the 'field' guy in my platoon salutes an officer with his left hand while holding his rifle at attention while in formation....

The only time this ever happened to me was while I was in Army ROTC during college.  The Marines were doing a recruiting drive in our student center.  Two of their Officers had just exited the building and I was walking towards them.  I rendered them a crisp salute, and they looked at me and just kept walking.  I held my salute till they were about 6 paces behind me before dropping it.