Not very. It is something else you have to carry, in addition to your phone and/or tablet.
I want my phone to be that device. It has all that i do everyday that isn't code. Drop my phone next to a capable display and keyboard And I want to be ready to get my pics documents and the like.
To be honest this is what I thought/ hoped the whole windows metro was going to be between phone/surface/desktop. I guess I will wait and dream for apple to innovate this.
Maybe, if they can get access to a suitable display, keyboard, mouse.