Apple Dock hanging + no cmd-tab or Expose

Last week my MacBook's Dock started hanging. At the same time I am unable to use the cmd-tab keys to switch between applications, and Expose does not work either. Quite irritating...

I used the Finder icons on the desktop to navigate to the Activity Monitor under Applications, and searched and killed the Dock app. It started up automatically again and worked fine.

I have a suspicion that it is related to network mounted drives, but this is unconfirmed. Next time it happens I will do a sample of the process to see what it is busy with. If anyone has any idea what this is about, let me know!