Mountain lions are growing in population, at least here in California (where voters banned the hunting of them in 1992). I had only seen one in my life until I was 23... I have seen four since then (I am almost 26 now)... and I have been exposed to the outdoors my entire life. They are very elusive and since hunting has been banned they really have no natural predators... which makes them pretty confident. I have caught a mountain lion stalking me in deep brush once and it was pretty unsettling... luckily I had a handgun with me that time... just in case.

If possible, avoid very thick brush in wilderness areas. Always check your back trail, because as previous posters have noted cougars do stalk their prey... mainly because they (like most cats) have very small lungs and thus weak stamina... they can only sprint at full speed for short distances.

If confronted by a cougar, be as large as possible and make a lot of noise. If attacked, fight. Cougars don't like to pick fights they cant win, so act like a more vicious predator.