My experience has been: * Google: Delivers incoming messages to whichever client most recently talked; occasionally 'resets' and delivers messages everywhere u

My experience has been: * Google: Delivers incoming messages to whichever client most recently talked; occasionally 'resets' and delivers messages everywhere until a client talks again. * Facebook: Delivers incoming and outgoing messages to web client; incoming messages only to XMPP clients (i.e. no outgoing message sync); occasionally outgoing XMPP messages are never sent or recorded at Facebook (this seems to happen and then stay a problem forever), resulting in your messages being silently lost.