I have followed this article to create a cross site Collection top navigation and it works greate.
http://msdn.microsoft.com/en-us/library/bb897739(v=office.14).aspx
I go through all Site Collections and add them to the top navigation. Now I want to hide one or two of the items (nodes = site collections) based on users Office profile property (office property contains the location of the user). I have created an Audience in CA but I don't know how can I implement it. Thanks for your help.