I agree with the AD part. A lot of the comments in this thread seem to focus on applications. Sure, that's a little bit of an issue. MS Office is a good example

I agree with the AD part. A lot of the comments in this thread seem to focus on applications. Sure, that's a little bit of an issue. MS Office is a good example of that. But applications aren't the main roadblock at this point - most things are web based these days anyway. And I'm sure with enough work you could setup a perfectly acceptable user environment, too. What I'm surprised not to see mentioned are the management capabilities - things like group policy, SCCM, WSUS and the like. I just can't imagine trying to maintain a fleet of hundreds or thousands of linux desktop computers. I imagine it would be like herding cats.