I'm not quite sure what the mood of this thread has evolved into, but I would like to contribute a little more of how I came to give my answer.
At least in my experience, I would say, "Thanks for your concern." in a totally different venue than an academic one such as this Forum. "Concern" is a word, in my mind, that's a notch higher on the emotion scale than for thanking someone for answering a grammar question.
I would be "concerned" for someone if the question involved some kind of sympathetic theme, such as a painful encounter or a grief Forum, or something having to do with a more comforting type of atmosphere.
If I replied in that type of situation, I would certainly be offering my concern - and it would be sincerely given, too. I would also expect a poster to reply in kind, "Thank you for your concern." The emotion would fit the circumstance for me then.
That's why I offered my list of suggestions to Kenny that I did. Those replies "fit" the feeling of the event.
I hope I'm expressing myself clearly, and that you realize that it's just my opinion and I respect everyone else's opinion, too.
Thanks for your understanding. (See, Kenny? Here's another example that's totally different from the rest of the ones I suggested this morning.) 
AngelEyes