Are you using PKI in your infrastructure?

With the increased demand for stronger security methods through compliance such as PCI, FIPS, Common Criteria, and others, the need for in-house certificate creation and management is becoming more necessary. While Red Hat offers the ability to create a managed CA through IPA in Red Hat Enterprise Linux 6, as well as their stand-alone product of Certificate System, I am curious; how others are handling the need to manage complex certificate management requirements? For what purpose are you using certificates? Simply for SSL encryption? Server certs? Signing emails? Identity management?