100, three times. Each time the main runs ("singles") totaled 85 and extra easy runs ("doubles") totaled 15. Once right before XC season started my sophomore year in college, twice the next summer. Both times I started at about 60 and added 5 per week until I got there. That second season I averaged 88 per week from July to October.
What did it do for me? Well, I've always been a slow runner (4:56/10:23 in HS), but it made me, um, less slow. I was 29th out of 30 on a middle-of-the-road D-I XC team as a college freshman, and as a junior I got as high as 11th.
Since I got old and fat my best was 78, 76 of it in singles, in early February of this year. Most of my weeks were above 70. What did it do for me? Made me ready to run a pretty good ultra. Unfortunately, I was getting ready for a marathon. I'm enough slower now that those 76 took considerably longer than the 85 did when I was 20, and it had a completely different effect. I guess you live and learn.