Quite a few, actually. For small-scale stuff it can pay to outsource. Really depends on the workload, and where the 'users' are.
But, once your core infrastructure gets big enough, putting a few more racks in the DC and adding a few staff versus now having to manage a 3rd party service with the same added staff becomes extra overhead and burden.
Also, some stuff may not due to legal or contractual obligations be feasible to be placed at a third-party site. (Verify THEIR staff as well as YOURS conform to standard, and two companies' policies, etc)