~/Library/Logs/CrashReporter/MobileDevice/<your iPhone’s name>/
C:\Documents and Settings\Application Data\Apple computer\Logs\CrashReporter\<your iPhone’s name>\
C:\Users\AppData\Roaming\Apple computer\Logs\CrashReporter\MobileDevice\<your iPhone’s name>\
C:\Users\<your username>\AppData\Roaming\Apple Computer\Logs\CrashReporter\MobileDevice\<your iPhone’s name>\
It's based on http://bjango.com/help/crashlog/