Mark,
First, let me add my sincere condolences. Your daughter's story had a profound effect on me. I live in Wyoming, only a few hours from the crash site, I help with SAR work, and I have a young son and a 9-year-old daughter. It broke my heart to learn the details surrounding the crash, and I can't begin to imagine the pain you have experienced as a result of all of this.
I agree with Flynengr's statement above and Rob's statement about pax briefing. The biggest practical impact this has had on me is that (i) I take the time to tell my passengers what to do and how to do it if they need help and I'm incapacitated; and (ii) I intend to upgrade to a 406 ELT (in addition to the SPOT I already carry). Like many others on this board, your daughter's situation left me feeling totally helpless at the time, but determined to try and make sure I never put myself, or my passengers, in a situation like that. Ultimately, the responsibility begins and ends with the pilot. However, all of us, whether high-time or just beginning, are still learning each time we fly. Consequently all of us, whether high-time or just beginning, will make mistakes at one time or another. Sadly, some mistakes cost much more than others. How we plan, how we fly, how we communicate, the equipment we carry, and the decisions we make can all help us avoid mistakes. Of equal or greater value, however, is the role those factors can play in helping to keep the cost of our mistakes as small as possible.
I commend and respect you for wanting to help make changes to avoid another terrible situation like this. You have already advanced that cause by initiating this discussion. However, I strongly agree with the previous posters that government regulated flight plans are not the answer we need. Instead, I think it is much more important that pilots think about and internalize what lessons we can learn from this tragedy (I still remember the float plane video too, which did a very effective job of delivering the message). Properly briefing pax, having the right locating equipment and survival gear, communicating our intentions--all of these things are important and tangible lessons that can be taught, internalized, and benefited from much more than any supposed benefit from additional government regulation regarding flight plans. I would urge you to pour your efforts into educating other pilots about the impact of their decisions on their non-pilot passengers and those left waiting at home when the plane turns up overdue.
I also think it is important that we continue to have a constructive dialogue about how best to help those in need, without the discussion devolving into a shouting contest between pro-CAP and anti-CAP mobs. I'm not pro-CAP or anti-CAP. I just know if it was my little girl out there (something I have thought about many times since this tragedy), I would want everyone available doing everything they could to find and help her in the most effective manner possible--and I would want the discussion about how best to do that to have occurred long before, rather than on-the-fly in the middle of the emergency.
I hope you are able to take some small comfort in the fact that your daughter's story, and this discussion, have already had an important impact on many of us out here and how we prepare for our flights. Once again, I'm very sorry for your loss.

