Call me
when you can run AutoCAD. Not another or similar CAD package, but AutoCAD itself.
Call me when I can manage a fleet of desktops and laptops with tools like Active Directory, Group Policy, and System Center.
Call me when our customers change all their contracts from specifying we use "Microsoft Office applications" to include the phrase "or compatible substitutes'.
In short, call me when Ubuntu meets our business requirements, because I'm not choosing an OS based on what games it supports.