Some call Google Wave the next big thing on the Internet while others think that it does not add anything new or exciting to the web. Whatever it is, most users have not had a chance to test Google Wave as Google has closed registration for the service. The Google blog announced yesterday that they will open the service to a new batch of 100.000 users. Registrations on the other hand remain closed and the only way users can grab one of these invites is by being a developer who have been active in the developer preview started in June, being one of the first users who signed up for Google Wave (and offered to give feedback) or by being a select customer of Google Apps.
Best chance for most interested users is therefor if they have filled out the registration form at the Google Wave website back when it was announced for the first time. Everyone else will have to wait just a bit longer before they can experience the service first hand.
Take a look at the video about Google Wave if you have not heard about it before: (it's long)
Your best bet currently is to signup at the website as soon as possible for a chance to be included in one of the upcoming invitation rounds (it is likely that there will be more or that Google will let users who have registered join eventually).
Update: Google announced in August 2010 that it would retire Google Wave in April 2012. The service was read-only since January 31, 2012 until it was shut down in April. Users were able to export their data as pdf documents in that time. Starting from April 30, 2012, it is no longer possible to do that or access the Google Wave website at all. We have removed links pointing to the service from our site as they point to a destination long gone now.