It could work well for temp stuff like an instant keyboard for a handheld, or very occasional typing. I doubt I would use one though. As an author I like the tactile feel of hitting the keys as opposed to fingers on a flat desk. If nothing was there it would break my concentration while I was trying to keep up with what my characters are saying.
Sort of the same for online shooters or other gaming. The traditional bumps, ridges, edges or keys let my fingers know where I am and where the other keys are. That isn't there for a virtual so I would always be looking down at the desk to make sure I was in the right place. I haven't used one but that's my impression.