Hi,
Since this thread started OS X 10.8.2 has been released.
In the iMessage Account pane in the Preferences some things have changed.
The Account Details button is now called Details and the Sign Out Button in on the main pane.
Your iPhone Number now gets added to the Receiving IDs (if you allowed it at the iOS 6/OS X 10.8.2 update)
Also you can also state which ID or iPhone Number to "Send" the message from.
The "-" button at the bottom of the List will not work to delete the iMessages Account (Only Sign Out and removing it from Details (which allows a new or re-added name) does that.)
As a default window the Messages window shows you nothing in it's normal view (other than any Logged in Accounts (AIM, Jabber, Yahoo) that have separate Buddy lists.)
The icon in the top Left pane creates a "New Message" and it then dispalys a blue icon top right
This Blue iCon gives access to Contacts (the Former Address Book) or Buddies
The "Groups" item you can see are the ones you may have set up in the Contacts app.
Useful for setting up a group of iMessage people.
The Messages Menu > Accounts will tell you if the iMessages Account is Enabled (Other than the box on the Account pane).
As you are saying that Apple ID is logged in for iMessages on other computers are you actually getting any sort of alert/error message ?
7:56 PM Saturday; November 10, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously