I remember all the rave about Microsoft's Holo-Lens, which had a similar idea to them. The biggest fault they had was that the field of view was way too small, so you couldn't really see much of what the lens were showing you. However, Google Glass seems to have the traditional glasses setup with proper angles. It also appears that only one lens will be able to see the hologram, too, I guess so you can look past it with your other eye(?).
Still very neat technology, but I think it has a long way to go before we can use it for every day purposes.