The document discusses four things the author learned while creating their first iPhone app:
1. Core Data - The author used Core Data for language and phrase data and found it slightly confusing since they knew SQL well. They used code from Matt Gallagher to make fetching data easier.
2. Progress Monitoring - The author added progress monitoring to show file copying progress, which took 20-30 seconds. They used MBProgressHUD.
3. Debugging Archives - The author hadn't been archiving dSYM files needed to symbolicate crash logs. They created a script to automatically archive dSYM files for release builds.
4. Version Numbering - The author used a Ruby script to generate increasing version numbers from