Today I noticed there are a LOT more settings available in the Power BI Admin Portal than the last time I checked. Here are all of the choices currently available:
Keep in mind that the above selections apply to all users across the entire tenant. At this time we can't control them by groups or anything of that nature.
In addition to the above settings for controlling user experience, the Admin Portal is also the place for viewing usage metrics which are helpful for determining who runs what how often (it's not everything we could possibly want to know, but it's a start).
The other two options, Manage users and Audit logs, redirect you over to the Office 365 Admin Center.
Getting to the Power BI Admin Portal is done from the gear menu at the top right of the Power BI Service:
If you don't see the Admin Portal or Manage Gateways menu items, that's a permissions issue. Until last month (Oct 2016), you needed to be an Office 365 co-administrator to be able to view the Power BI Admin Portal. That's pretty high level permissions, so thankfully Microsoft has released a new "Power BI Service Administrator" role for delegating the Power BI administrative portion. Info about the new role is here: https://powerbi.microsoft.com/en-us/blog/making-it-easier-to-administer-power-bi/.