I have an AD group called SQLAdmin. I have set SQLAdmin up in this way:
SQLAdmin - Browser, Content Manager, My Reports, Publisher, Report Builder
I have set up System Roles like this:
System Administrator
Execute
Manage (jobs, server properties, server security, roles, shared schedules)
System User
Execute
View (report server properties, shared schedules)
I have a user in the SQLAdmin group who does not see the 'Report Builder' link. I am not a system admin, but I am in the SQLAdmin group as well, and I do see the 'Report Builder' link.