Adding Debian Sid as Package Repository?

You're mixing two different distributions' packages together. For various reasons, this is a bad idea:

Security.
Stability.
Conflicting updates, which you have right now.
If you let above updates go through, you encounter the first two problems, and then you're in deep trouble if say, as an example a kernel update comes through!

Also, this makes getting an accurate bug report or stacktrace almost impossible, if not entirely impossible.

In short, if you need Debian sid, run sid. Otherwise, run Ubuntu, and just add newer software you want to via a PPA or backports.

More explanations here:

This might be necessary if you need a package currently not available in your ubuntu release.

My suggestion is to use apt-pin.

I created /etc/apt/preferences.d/unstable with following content

Package: *
Pin: release v=12.04, l=Ubuntu
Pin-Priority: 1000

Package: *
Pin: release a=unstable
Pin-Priority: 600

This ensures that the basic distribution always takes precedence. In case a package is not available, unstable is chosen.

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