Siri can no longer find my home #
I had similar problems, only Siri was not finding contact information of any kind, was not locating my friends, and not opening apps on command. I found that the problem was that Siri was having an issue with opening apps was causing all problems listed. To fix I used a Cydia app called iFile to locate the following files:

/var/mobile/Library/Caches/com.apple.LaunchServices-045.csstore
/var/mobile/Library/Caches/com.apple.mobile.installation.plist


Delete both the files, close iFile, and reboot device. After restarting all your apps will be gone and they will come back one at a time. Took only a few seconds for them all to load. Tested Siri and all my problems solved.

I'm using a jailbroken iPhone 5 with 6.1.2