Sometimes if you have a crash we cannot duplicate we can get the crash logs of our apps from you.
iPhone crash logs are copied to the following directories on the user's computer by iTunes during sync.:
On Mac OS X they are located in ~/Library/Logs/CrashReporter/MobileDevice.
Windows XP: C:\Documents and Settings\<USERNAME>\Application Data\Apple computer\Logs\CrashReporter/<DEVICE_NAME>
Windows Vista: C:\Users\<USERNAME>\AppData\Roaming\Apple computer\Logs\CrashReporter/MobileDevice/<DEVICE_NAME>