I just returned from a two week trip on the Alaska highway with my 80 year old mother. I was pleasantly surprised at how much adventure we were able to squeeze in; tour companies are doing a great job with mobility issues. We found bus and boat tours were very willing to accommodate a wheelchair and took extra care to make sure my mom saw the special sights.
I've summarized a few of the experiences on this video

http://www.youtube.com/watch?v=zOAH1I6tAF0

I'd be curious to know what other people have experienced when traveling with people with limited mobility.

Carol