Lydiard,
That is exactly correct about the Kenyans and exactly what I had in mind when I searched out Lydiard's principles and John Molvar. In my case its not like I have no base either... I mean I was a runner for 8 years throughout hs (averaged about 20 a week) and college (maybe averaged 40 a week throughout my 4 years... with weeks as high as 90 and 100, and as low as 0) and had moderate success (more in training runs than in racing, but that is another story all together and deserves a whole thread on mental ability - or in my case, lack thereof once I got to college).
But, allow me to address the question at hand... doubles versus singles.
The way I see it is the more mileage one can handle in singles the better. If he/she can't handle singles, though, then start breaking up the runs. Its as simple as that. Do as much as possible in one run a day and go from there. There are definitely biological reasons why one longer run a day is more beneficial to a runner... from recruiting fast twitch muscle fibers to increasing the size of muscle mitochondria.
I also tend to think 1-a-days fit into a working person's life much better than 2-a-days. Why do 2 runs and be tired from waking up early when you can have 1 run and sleep in a bit? That 1 run will be a more quality run than either of the 2 runs just based simply on bing more rested.
M