Question of the Week: To Host or Not to Host?

This is a question for Hosting Companies.  If you could choose any service that you offer your customers today and have a third party provide those services to your customer instead of yourself.  What service would that be?  Would it be mail?  Would it be streaming services?  Would it be everything? and Why?

 I am really trying to explore the core services that hosters really want to focus on and determine which other services are simply fringe services that are there to supplement what the hoster offers.