How do I temporarily disable or mute Messages (iMessage) on OS X?

I use Apple's iMessage across several devices, including my (OS X Lion) Mac, using the recent Messages beta.

However, the application has some undesired behaviour.

When I quit Messages, it will relaunch itself when I receive new messages. This is incredibly distracting.

Is there a way to temporarily disable or mute iMessage (including the badge on the Dock) from just my Mac? I'd still like to receive messages on my other iOS devices.

An update for Mac OS X 10.9 (Mavericks). You can turn on Do Not Disturb in Notification Centre to mute notifications:

You can show Notification Centre by clicking on the three-horizontal-lines icon on the far-right of the menubar, or perhaps by doing a two-finger swipe from the right edge of your trackpad (if this gesture is enabled in System Preferences -> Trackpad -> More Gestures). Then swipe up to reveal the 'Do Not Disturb' toggle (which is hidden at the top of the notification centre panel).

Update: I've also just discovered that you can option-click on the Notification centre menubar icon to toggle Do Not Disturb mode on and off.

Click your apple symbol in the computer -> System preferences -> notifications -> messages -> none

On the Messages menubar, go to Messages-> Accounts and uncheck iMessages.

In Messages, unselect the "Use Alerts in this Conversation" option in the View menu. This should enable iMessages without the sounds.