Today (30th September) Google will be releasing more than 100,000 invitation to.
Developers who have been active in the developer preview we started back in June
The first users who signed up and offered to give feedback on wave.google.com
Select customers of Google Apps
Further describing the Wave key features
"There are also still key features of Google Wave that we have yet to fully implement. For example, you can't yet remove a participant from a wave or define groups of users, draft mode is still missing and you can't configure the permissions of users on a wave. We'll be rolling out these and other features as soon as they are ready — over the next few months."
Google Wave will be another cool thing that can change the way we interact with people online and via social networks.
Official Google Blog: Surf's up Wednesday: Google Wave update