Directory Services, GP, enforcement and Package management.
The only thing preventing me from really jumping into the Linux World is a robust Directory Services (such as Active Directory DT, UC) and a group policy/ enforcement suite (such as GP and SCCM). I like the direction of the Linux Community, but without AD, GP and an SCCM like applications I will never be able to employ it in a robust small-medium business network environment. (LDAP only goes so far, and without policy and health baseline assessments and enforcement a significant percentage of my potential Clientele is off limits, meaning loss in revenue streams for my business).