I've only left before the end once, but not at intermission. I went to a Saturday matinee of The Pirate Queen. I was planning to leave at intermission, but on my way back to the subway, I stopped at Grey Gardens to buy a rush ticket for the evening show (they'd just gone on sale about 20 minutes earlier, at 3pm). After being outside in the wonderful May weather and listening to the Grey Gardens soundtrack on my iPod and thinking about how wonderful the show would be that night, I started to think "oh, come on, The Pirate Queen wasn't really
that bad, was it?" So I went back. As soon as the second act started, I was like, "Oh, yeah. Now I remember. It really is
THAT bad," so I left about ten minutes into the second act, as soon as there was a lengthy scene change and an appropriate place to exit. As I was leaving, there were two different groups of people coming down from the balcony (I was orchestra level) on their way out as well. One of the ushers in the lobby commented on her surprise that we had made it this far.
"I just want a story and a few good songs that will take me away. I just want to be entertained. I mean, isn't that the point?"