According to this post (which solved my problem): http://blogs.technet.com/b/mpriem/archive/2012/08/20/sharepoint-2013-preview-newsfeeds-showing-nothing.aspx
The solution and problem was :
"The problem in this case is that my MySites are hosted in a different application pool from my UPA service application.Although the MySites application pool account is added, the service app application pool account is not.Either grant the application pool account hosting the UPA Sharing Permissions through Central Admin
This describes my setup perfectly - one application pool running the MySites (and all web Applications) then a service Application pool running other services including the User Profile Service.
While the posters solution works very well I don't understand why you would need to add permissions to the service application pool account that is HOSTING the User Profile Service- shouldn't it automatically have full control if the User Profile Service is running as *that* application pool?
