Some of you may already think shared calendaring is a cloud-only activity, but I submit that lots of folks still maintain their calendar on a PC or handheld device, and struggle (as I do) to try to share it with others. One reason this habit persists is just inertia; another is that the cloud calendars by and large do not really provide a great deal more function than the standalone ones. Cloud calendars such as Tungle start to change that by making it possible to "paint" one's availability on a grid of times, effortlessly shared with other Tungle users.
But Google Wave seems to me to add something really exciting to all software, that is the ability to "play back" the history of any online collaboration, and it would seem natural to me to have a shared calendar where I could do exactly that, following the steps that may have led up to a particular event being agreed upon by various participants. That's just one example of what something like Google Wave can provide. So I'm left believing that whether or not Google has invented a standard way to do this (as they hope) or not, all shared calendars will eventually have this capability, so that you would not only have the schedule, but a history of how the schedule came to be.
The Google Wave demo at I/O this week didn't specifically reference calendaring, but the very first use case was a dialogue between two users trying to agree to attend some event together, so I don't have to think very hard to come up with "waves" whose end product is a shared calendar entry.
The immediate impact on calendar sharing is negligible, but the long-term impact is profound. Maybe I've drunk too much Google Kool-Aid at this point, but any calendar sharing solution that ignores this kind of collaboration ultimately does so at its peril. And having Google do it first probably means it will end up getting done the same way across the Web, and that would be a good thing, whatever my reservations about Google's own privacy policies.