Not for the faint of heart.
For more seasoned hikers, this seems to be a pretty popular place. Going on a weekend you'll probably encounter quite a few people going up and down.
My advice to the more amateur of us hikers: take your time. I feel that Summit Trail is a "trail" in a very liberal sense of the word. Save a few brief paths, most of the hike up is unpaved. The path is full of rocks that make going up (and back down, to a lesser extent) pretty challenging if you're used to more friendly hikes. You really need to watch your step if you don't want to hurt yourself.
The trail goes pretty far up. I stopped a little past halfway. I'll probably come back once I have more experience under my belt and the weather gets cooler.