Apologies if this has been answered elsewhere, but...
I have a Harmony 550, and I've been really pleased with it thus far. In fact, there is really only one nagging issue I've been having with it. It fails to turn my Samsung DTB-H260F ATSC tuner on/off about half the time. I often end up having to walk to the room that contains my rack, point the remote right at the box, and hit "HELP." I then proceed until it asks whether the DTB-H260F is on/off (depending on whether I'm powering up or down), answer "NO," and occasionally it still doesn't turn the box on/off (but after answering "NO" a second time, it works).
Sooooo... any suggestions? I haven't had any other problems with devices, in either device mode or activity mode. The DTB-H260F responds beautifully to all other commands, too. Just not power toggles.
As I mentioned above, I do have my equipment rack in a different room than my display. I use an IR extender (HotLink Pro) with the receiving eye hidden behind my front-right speaker grille, and dedicated emitters stuck onto all the equipment in my rack. I don't think this is a factor because, as I said, all other devices work fine and the DTB-H260F itself responds well to all commands but power toggles.