I'm inclined to think something has corrupted your preference files or application data, as those will be brought back after a restore from backup.
In order to test this theory, you will need to wipe the phone by putting it in DFU mode, then restoring to the latest Apple firmware through iTunes. Then set up your device as a new device. If the problems still occur (unlikely), then I would take it in to an Apple Store and have a Genius look at it.
If, however, it fixes the issue, then you will have to play "hunt and go seek" with the culprit. Restore your backup, jailbreak (but don't install anything from Cydia except OpenSSH so you can access the file system), and root through your "home" folder (/private/var/mobile).
You should try deleting the preferences (plists) first (~/Library/Preferences), then rebooting. Don't worry, iOS will recreate them. If that doesn't fix it, try removing the sqlite database in ~/Library/Twitter, although I have a feeling the preference files should take care of it.
I wish I had an easy answer for you, but it's going to take some study of the file system and tracing back to the package that "infected" your system.
Not everything in Cydia is deemed safe and you may wish to exercise more caution in the future. MobileSubstrate (which is only made possible be reverse engineering) provides the hooks for many deep level APIs that shouldn't be messed with.
Additionally, you may want to hit up jailbreakqa for additional help, as that is the official forum for help on these matters. From my experience, there isn't much help here regarding this process.
OK I've found out the answer myself.
It turns out that although the Maps app can geocode (find the location of) my address, Siri can't. It must be using a different geocoder to the Apple Maps app.
After much faffing, I found the easiest way to fix this is to drop a marker on my house using the Apple Maps app and then add this to my own contact record as "home". This fixes the problem and allows Siri to know where home is. However it then means my address is incomplete if I use it for other purposes or in other apps). The only way round this seems to be add it back and tag it as "address" (NOT "home") as a second copy of the same address. Really messy.
Clearly this is a bug in Siri which will hopefully be fixed one day (I won't hold my breath). I don't recall having this problem in iOS 5, so I think this was introduced in iOS 6.
Best Answer
Not everything counts from 1970. Its the standard time of Unix.
Unix Time
Why is 1/1/1970 the “epoch time”?