I love hiking barefoot. In the last couple days I've gone on some pretty extensive hikes and I've come across two things I really don't like stepping on: 1) Dead pricker vines hiding under soft leaves... they stick in your foot and HURT 2) Some kind of pine cone has "leaves" or whatever with little spikes on them to help them stick in the ground and root... those spikes are unwelcome jolts when wandering around in the woods. They don't hurt too bad but they definitely stick into your feet until you pull them out. My feet have been getting tougher and tougher, rocks and sticks are no match for me... the sharp stuff is still a pain though. What else bothers you guys in the woods?
Thorns hiding under dead leaves are definitely tops on my list. We have one variety here which develops 6-8cm-long razor-sharp iron-hard thorns that will go through the toughest soles (barfoot or shod). When I know they're in the vicinity I go veeeerrrrrryyyy slowly. My second most hated thing is Mimosa pudica. These nasty little buggers hide in grass awaiting the unwary barefooter. Even toughened soles can get the tiny toxic thorns embedded in them and then itch like crazy. Other than that, we're pretty well-off here in terms of lack of hazards.
Florida has these things which some locals call sand spurs.... They fucking suck - luckily, I've never stepped directly on them, but, they're everywhere from the beach, to the woods. They're spikey and clingy... No fun...
The time of year I dread the most is coming up...Fall. When the leaves fall, they cover the trails and all the little rocks, roots, and small tree stumps that make hiking difficult. I hiked 5 miles last Saturday and finally made it without my feet hurting at the end. Even after hiking 1/2 mile on gravel. I don't care for the Sweet Gum pods.
There are no particular hazards here in England, just thorns which can usually be felt before they do any harm. Nettles don't bother my soles, but they can sting the tops if i don't tread carefully among them. I once got lost in a small forest because fallen leaves (nice to walk on!) covered the footpaths. I've carried a compass ever since!
I hate dog crap on the trails, I wish the owners would take some responsibility when they are on public property. I've been tempted to pick it up and throw it at folks, but I don't. I haven't had the sticker or thorn problem here in the northeast, but I'm sure I'll run into them somewhere at some point. In the winter time re-frozen slush is brutal with a sharp edge on the top layer that can scratch your shins.
Crushed acorns and small, sharp tree branches bother me a little bit. I hate it when acorns and other nuts stick to my foot.
Tree roots at the very surface of the ground and various stumps really suck. I stub my toes on them much more frequently than I'd like to, especially in the darkness.
My mom seems to think I'll step on a hyperdermic needle contaminated with AIDS (well, maybe not AIDS, but she's afraid nonetheless). Or glass. Or a nail. She's only afraid of this for when I'm on the grass, though. She isn't afraid when I'm on the sidewalk, because then I can see where I'm going.