I took my hybrid, a rigid aluminium trek with 35mm tyres, down to the various unpaved roads and paths near the river I live. Much of it was just gravel road with potholes, and depressions where muddy water had gathered, but some of it was some very deeply rutted forest paths, no roots sticking out though but still pretty bumpy. The kind of thing you'd need a 4wd to go over.
All 'n' all, I very much enjoyed this sort of mild off-road stuff. I thought it was just right for the sort of bike I was on (though I'm a heavy dude and did worry about the wheels...)
Anyway it got me thinking - what's the roughest stuff you'll tackle with a hybrid? Photos would be nice - I apologise for the lack of my own, might see if I can borrow a camera at some point.