I did this for a couple years, but as a triathlete, not just a runner. It's a pretty decent life, if you can handle not being a social butterfly. I did at least 2, most times 3 workouts a day during the summer. Spent a lot of time sleeping, and really had to eat constantly (4000-5000 calories/day) to support all the work. I had a full time job but no social life.
A typical day might've been swim 5:30-6:30, get to work by 8:00 at the latest, then bike and run after work..say, 8 miles run, 30+ miles bike, etc. Lots of daylight in the summer. The running volume never exceeded 60mpw, but there was several hundred+ cycling in there. Often to make mileage totals, I'd race Saturday AM and then run that night as well. In bed by 9:00 usually. I took it to extremes - for example, knew I had to race in summer heat, so I decided to live without air conditioning (even though I had it) to condition myself. It was well over 90 in my house most of the summer (you get used to it).
I often did speed work on Tuesday night, then raced on the track (800-mile-5k) on Wednesday nights, then I would do a triathlon on Saturday. The back-to-back hard days worked well for me.
This was by far the best shape I ever got in - I was running tri splits (5mile, 10k, etc) faster than my road PR's at those distances. The work paid off - I went to USA nationals.
Then, the injuries set in.....but, it was a glorious time.