Back in the years after college when I was actually training, I finally figured out that I only "needed" to run intervals if I was gearing up for important shorter races - 5K and shorter. This flew in the face of everything I learned in college - that intervals were KEY for success in distance running, including all those 8K and 10K cross country races. Man we ran a lot of repeat Ks, 1200s, and miles, and all at REALLY hard intensities.
Anyway, in the time I was in grad school, I usually could pop off a 10K in the mid-high-33s, and I was putting in weeks like:
M - relaxed 7-10
T - usually a "hard" 8-10. Start easy and build into an "extemporaneous tempo run" as John Kellogg calls them now
W - easy 3-4 in the morning and several hours of racquetball at night
R - relaxed 5-8 (several hours of racquetball leaves one sore)
F - "hard" 5-6 (6-7 with w/u and c/d). usually about a half mile warm up and then get right into it, with some kind of loose time goals, but the idea to hold the same pace for the whole run, then half mile cool down
S - easy 8-10
S - 90 minutes of whatever I felt like. Sometimes that was 7 min pace for 13ish miles. Sometimes I would slowly ramp it up and turn the long run into a long sustained modified tempo run - I guess it would most closely approximate a marathon pace run if you want to label it.
In addition, I was hitting the gym 2 days a week, and doing some racquetball drills 2 days a week for about an hour each time.