I installed QtCreator and Android SDK/NDK into a Vbox running Unbuntu 12.4. Although my Nexus was physically connected to the PC, I forgot to connect the Nexus to the VBOX USB controller. Subsequently running adb hangs forever.

Unfortunately I only realised this much later. I actually experienced a hanging Qt Creator. Only after I debugged Creator I discovered that the cause was a hanging adb.

QtCreator should not freeze despite adb hanging.