umm.. reasons to switch for what role? server? development platform? desktop?
I'd be hard-pressed to advocate the Linux desktop to the masses yet..
And in many other situations, the TCO (Total Cost of Ownership) for Linux would be too high in the short term for me to convincingly advocate.
That said, I think the progress is pretty darn strong.. if you are trying to get your organization to let _you_ switch for yourself, that's a different arguement than trying to argue for someone _else_ to switch. The burden of proof to get someone else to switch is _so_ much higher.
Besides.. it's a lot easier to get people to "try" than to "switch". It takes very little for me to try a new OS (or nearly anything), but if you want me to _switch_ to it, I am instantly defensive. It's a conditioned response I suspect many people have.