Yes, very frustrating. Used to be limited to the more technical parks...Now I see this at less technical parks like Lew Mo and 6MR. In fact, just YESTERDAY...I was stopped on top of a small hill at 6MR adjusting my helmet. The section I stopped at had some exposed roots, but nothing nasty. I was off the trail, so riders had plenty of room to pass. Along comes a guy up the hill towards me, sees me, we say hi, and then he proceeds to completely avoid the rooty section and cut through a short section off to the side of a tree bordering the rooty section. I look down at the section after he's gone and can see he isn't the first to have done it (lot of leaf compression on the ground cover).
I looked around for the nearest large-ish log and promptly put it down lengthwise on the cheater line to hopefully disuade others. But it boogles the mind that, despite purchasing and riding bikes that are built for these trails (suspension, gears, etc), some riders just want to take the easy way around things. Isn't part of the appeal of mountain biking the challenge of tackling uneven terrain? :hmmm: