The longest streak I ever did was the Marcothon challenge which involved running every day in December for at least 3 miles. I did it a couple of years, but I found living up here, the weather conditions were the hardest part.
I once did a nine day streak of long distance running, by the end my ankle was quite painful and an X ray a few weeks later revealed that I'd been developing stress fractures. I certainly wouldn't have been able to continue for many more days.