Hi Nick,
I was training for my 1st Marathon recently I will honestly say that having to run Time Ratio's of 2/1's and 3/1's seemed very constrictive. I didn't like them! Especially If your a person that really want's to be able to Run enough to know that you accomplished some distances during your run.
I have been using the Run/walk Ratio's for a couple of years and have found that I could get the same results using 5/1's or 10/1's But after awhile if you use any kind of timer watch, you may find your self tied to the Bells and chimes to tell you went to run and when to walk? Can you get any kind of enjoyment out of your Long Run or Race?
So I have switched to using more of a Distance Ratio I could set my Garmin to a certain distances of either 1/2 mile, 1 mile, 1 1/2 miles and or 2 miles. Because I read that most Marathon will place their water/aid stations at about 1 1/2 miles to 2 miles.
But recently I have felt more "Freedom" to choose my own Distance on my Routes. I run to land marks such as houses, or a specfic street. I know the approx distance from previous messured Runs. But I find that is more Fun to Run

when I don't have some Blasted Beeper telling me what to do!
True, if your a "very" fast Runner to be able to Run fast during the 2 minute Run segment that's Great! But if you a very slow runner like me I think that the 2/1 ratios would slow me down with more fustrations of not getting anywhere than any over all improvement.
But that's all my 2 cents worth... it's really up to what you want to do?
Forestina