Here what Google Says :-
Wave has not seen the user adoption we would have liked. We don’t plan to continue developing Wave as a standalone product, but we will maintain the site at least through the end of the year and extend the technology for use in other Google projects. The central parts of the code, as well as the protocols that have driven many of Wave’s innovations, like drag-and-drop and character-by-character live typing, are already available as open source, so customers and partners can continue the innovation we began. In addition, we will work on tools so that users can easily “liberate” their content from Wave.
You will be able to use Google Wave service only this year.