I'm trying to think of famous tourist destinations so crowded that I wouldn't want to go visit it. The only things I can think of are places not worth visiting in their own right. Washington DC with its lines for the Monument, Capitol, and seeing the Constitution come to mind, but easily avoided by coming in the fall when no school kids are kicking around
I've been to 8 of the ten here and don't recall the crowd being an issue.
Then again, when did the Lonely Planet ever get anything right?