I have an X1 Carbon 2014 model, and everything seems to work great on Ubuntu 14.04. Recently now I've had to use it twice to give a presentation, and both times it's failed to detect the VGA projector. I've used it at home with both a VGA and a DVI monitor and it works fine. I'm using the Apple VGA and DVI mini displayport adapters, which I've used for years on an old Dell with MiniDP and now with the X1 Carbon.
When it comes to projectors though, the laptop refuses to even acknowledge that the projector is there. I can plug it straight into a monitor with the same adapter and it works fine.
I'm kind of at a loss as to what to do.