When using Xcode 4.2 for iOS development there’s an annoying bug where any exceptions crash to the main.m file instead of highlighting the line. Luckily you can set a custom breakpoint to restore the old and correct behaviour:

1. Open the Breakpoint navigator (CMD + 6)
2. Click the + button in the bottom left
3. Select Add Exception Breakpoint 
4. Click Done

Voila!