DMGLong Run = 1/3 of Weekly Mileage
I hadn't heard this rule before, and I don't want to forget it:
Your weekly long run shouldn't comprise more than 30% of your weekly mileage.
I've realized that things go smoother when I get in three runs a week, but I never thought about the proportions, or came up with this kind of formalization. Good rule.
I do, however, realize that if I want a 10-mile long run, I'm going to have to put in 30 miles per week, which (for me) is a lot. I think my original routine of running three runs with the long being double the length of the short run worked because I was effectively cross-training so much. Hockey, swimming, and weights combined to make up that other 1/3 of my weekly "mileage."