A couple of years ago I hiked Mt. Marcy in July. Here is a small excerpt from that post:
When I finally got within a half a mile of the top, the weather became outright inclement. I had read about people dying on Mt Washington in Maine (6,288 feet high) during freak snowstorms in the summer and I could never understand how that can happen at such comparatively low altitude, as judged by a Californian. On Mt. Marcy I got my enlightenment. Even though I wore every stitch of clothing I had brought (my T-shirt, my long-sleeve hiking shirt and my windbreaker, I was whipped by an icy storm. Frozen raindrops pelted me sideways from the west. I had to face away from the wind so my hood didn’t get blown off and I could see. And through this I was picking my way up sheer rock slabs, slippery from the water, steep and sometimes without any good footholds.
Then, just recently, I came across this horrific blog entry that shows what can happen to a lone hiker. He got lost near the peak, but it was in winter. I cannot even imagine the panic he felt, and the fear for his life.
I always carry a GPS now. If I ever lost my way, I would notice it quickly and I would be able to determine where I missed my turn. It could quickly backtrack. This saved me a couple of times when hiking up on Half Dome and getting lost in the darkness of the early morning.