Google Wave is now being actively migrated to open source and the code is at a level where I think it may be ready for trials on a SheevaPlug. Basically, senior management at Google decided that offering Wave to the public was not worthwhile. The Google Wave team members are making an earnest effort to migrate the code and/or technology out of Google's vault into the open source. Of course, they probably have certain plums that Google wants to retain, but I think what I have been seeing in the last few weeks merits mention in this forum and alerting early adopters of a possible new technology for the Plug.
I run Gentoo on my Plugs and the free Java support for ARM is just not there, I cannot say that there is a Gentoo/Plug ready solution for Wave at this time.
However, for the bulk of you who have more generic Linux systems running on their plug, if you have Java, then you may want to start trying out the rapidly development Google Wave Protocol (the name of the project which is basically the open sourced version of Google Wave) at:https://sites.google.com/a/waveprotocol.org/wave-protocol/wave-in-a-box/setting-up
The current code, e.g. build 629, is not ready, but the development is at a stage where you can have a server running that will have client code that is starting to look like the Google Wave client currently offered by Google. Note: Google is abandoning Wave and has warned that they will be terminating the service at the end of this year.
If you have your plug running in a community/corporate environment, then you might want to consider trying out the code and evaluating whether this project may have some merit down the road.
I guess what I'm trying to say is that if you have a Plug that runs Java and want to see what your plug can do in terms of providing a nifty collaborative tool, then take a look at Wave and report your findings in this forum.