Google in their August 4th update states that:
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.
Update on Google Wave
The failure was primarily due to the business decision to launch the product too soon. This was a robust application whose target audience included non-techies who will have nothing to do with a product that doesn't help them accomplish the tasks at hand. In many ways Google Wave was a time-sink, entertaining and a useful exercise for IAs, developers and other techies, but of little to no use for many business users. The end result we see now - after a rousing introduction - Google Wave is dead barely a year after being introduced to the public.