We were expecting this after it was announced Google bought over Meebo, but here's final confirmation.
Of interest to librarians, Meebo Messenger, Meebo Me, Meebo Mobile Apps will be shutting down July 11th, 2012. All embeded widgets will stop working and you can download all chat logs at https://www.meebo.com/chatlog-download by July 11, 2012.
For more details see http://www.meebo.com/support/article/175/
Meebo Bar will continue but I don't think many libraries use it. Meebo Me widgets of course are used by many libraries to provide IM reference support.
Other free chat widget alternatives exist including AIM, Chatango, Plugoo , Gtalk etc.
EDIT : Others I see mentioned include Zoho Chat, ChatWing, Digsby , Spark
Depending on your needs you could get away with free accounts on Zopim, Olark etc though you probably will need to pay if you use the service heavily.
Library specific IM reference services exist of course include Libraryh3lp , OCLC's QuestionPoint and SpringShare who offer the popular LibGuides is readying LibChat.
Or perhaps in the age of Skype, Google Hangouts, SMS ref, Twitter & Social Media, IM reference is no longer so necessary?
Are you impacted by the closure of Meebo? Let us know in the comments.