SharePoint 2013 Following Sites

Pro-Tip – when you’re setting up your 2013 farm and the ‘follow sites’ features don’t work between web applications…make sure the web app’s app pool account has SPDataAccess rights (that’s one of the new schemas in 2013 in the databases) to the content database in question.

See this blog for more details:

http://mrhodes.net/2012/07/31/sharepoint-2013-follow-not-working-across-web-applications/