When installing the SDK on native Ubuntu 12.04 64 bit it can happen that Ubuntu will freeze completely.
This is a known bug.
To install the SDK correctly type from the Terminal; ./QtSdk-offline-linux-x86_64-v1.2.1.run -style cleanlooks
In this case i'm using the Offline installer but this also works for the Online installer.
note: you don need the Qt SDK for Q7B but i'm using Qt Creator and that is why i install the SDK.