Great question - and yes, there is new functionality that came out in the last release (Winter '12). Hopefully you are using LMA (License Managing Application) with your Managed Package. If so, starting with the Winter '12 release, you will see a new tab called Subscriber Support (or maybe just Subscriber...). Click that Tab. You will see a record of each customer which has installed your managed package. If the end customer has granted you access, you can login on their behalf. Once logged in their behalf, you can open up the Sytem Log Console , run the specific test case, and the debug logs output in the System Console will show you System.debug messages (since the system knows you are the ISV logged on their behalf).
In the online help, search for Subscriber Support or Package Support Access to read more about this functionality.
Refer these links
http://salesforce.stackexchange.com/questions/142971/how-to-log-system-debug-messages-in-managed-package-beta-version
http://www.jitendrazaa.com/blog/salesforce/how-to-debug-manage-package-in-salesforce/
http://salesforce.stackexchange.com/questions/47145/debug-statements-in-managed-package
Thank you
All Answers
Kindly go through - https://success.salesforce.com/ideaView?id=087300000007Py4AAE (#)
In the online help, search for Subscriber Support or Package Support Access to read more about this functionality.
Refer below links for more info
http://salesforce.stackexchange.com/questions/12313/how-to-check-debug-logs-for-installed-app
http://salesforce.stackexchange.com/questions/142971/how-to-log-system-debug-messages-in-managed-package-beta-version
Hope this helps :)
Thanks!
Amit Singh
Refer these links
http://salesforce.stackexchange.com/questions/142971/how-to-log-system-debug-messages-in-managed-package-beta-version
http://www.jitendrazaa.com/blog/salesforce/how-to-debug-manage-package-in-salesforce/
http://salesforce.stackexchange.com/questions/47145/debug-statements-in-managed-package
Thank you