Found the limit!
I bought my Specialized Crosstrail last year and have been very happy with it. Commuted, fitness rides, trained and raced a sprint tri and duathlon, and even raced it in a mountain bike race, which was mostly gravel roads, and no tough single tracks. With its 700c wheels, and lockable light suspension fork, I could customize my ride by changing tires and locking it out.
Having bought a road bike recently, I felt I would use the hybrid more for commuting and trail riding. My buddy wanted to go to the local state game area for a trail ride. 2/3 of the ride went well, even though I hadn't ridden single track in 20 years, I was managing the limitation of the bike on the trail. Then it happened, a quick turn high bank where I caught a tree root, and slid down. Ultimately wiping out, and bending my front wheel. 32 spokes, mashed up and bent to the point of needing replacement. So, I guess I will be needing a mountain bike if that is going to be part of my riding.
Thanks to my LBS for hooking me up with a sweet new front wheel.