As you know, and I hope some of the readers recognize this fact as well, Henry Rono is a multi-world record holders from the late 70s and early 80s. He has run thousands of miles on his feet, way back I'm sure from his school-boy days. It's safe to assumem that he had developed tremendous oxygen carrying capacity. Lydiard always said that, once you've deveoped aerobic capacity, you won't lose it. What he means is not that he could get back to world-record breaking shape, but that you could very quickly get back to a certain level of endurance activities. From what I've read, I don't think he's very much concerend at all at what pace he's running those 2~3 hours, which is correct way to approach. Bearing in mind, he would not hurt himself from wearing incorrect shoes or too much unnecessary pounding, and he feels happy about the effort and not overexerting himself, I don't see any reason why this is not a good formula for him.
As for myself, I have recently gotten back to a twice-a-day routine; running anywhere from 25~45 minutes in the morning and 45~100 minutes in the afternoon with a long run on weekend (usually about 2 hours). My wife was worried about a sudden jump (I was jogging about 3~5 times a week for about 30~90 minutes at a time) but I feel quite happy about the effort and, in fact, I feel progress in my strength. I did make a sudden shift but I was confident that I could manage it. I didn't run much for about 5 years now but then again, I had tons of aerobic running (80~125 miles a week) when I was younger...and lighter! I'm careful of wearing the correct types of shoes and choose the surface of the runs. In fact, I'm having less leg problems now than when I was lighter because of that.