Only problem with summer hiking is the tourist population, so I try to avoid going out on the weekends. I go out for the peace and quiet, and after Labor Day, the Greens, Whites, and 'daks all experience a mass exodus when everyone goes back to school/work. September is THE month to hike. After that, the sleeping gets so cold. I sleep cold in my own house October-April (why do I still live in northern Vermont?), never mind a tent. Not to mention, it seems the mountain clubs are busily removing the woodstoves from shelters because people are irresponsible and set things on fire (did I mention that people are my problem? :)
That said, I still love being in the mountains in the summer--beats being in town where there's traffic and asphalt. But then, I don't really sweat unless temps are over 85* and muggy. And I don't mind sweating, just bring extra water and imagine it's a great big sauna.