I finally made it to the Gainesville-Hawthorne Trail in May 2014. I biked from Hawthorne to Rochelle (8.5 miles). Then I biked from Boulware Springs back towards Rochelle. However due to the steep hills and being out of shape I only did 3 miles. Info has this trail being 15-16 miles long. However the trail goes farther from Boulware Springs heading north towards Jacksonville. That might add 8-9 miles. Also there is no trailhead at the downtown area on SE Depot Avenue. This is a very scenic and mostly rural trail. My full review and lots of photos are on my website.
My wife and I ride it a couple of times a year.... trips to either my Cardio or EP Docs at Shands and sometimes to Trader Joe's. It's great trail and little narrow in places. Thanks for the write up. The trail selection in FL is AMAZING. The reason we moved to the area from Maine a couple of years ago.