I have been fooling around a bit with Google Wave. It is a rough application in the current Alpha form, but Google is promising a number of improvements including cool enhancements before moving the software into Beta.
The biggest limitation at this early stage is the lack of users combined with the inability to communicate via email using Google Wave. This restricts the pool of corespondents to include only those who are both already in one's Google Contacts or participants in a Public Wave AND people who have a Google Wave account. At this point, for me, that is 12 people--many of whom got their account because I sent them an invitation. Until these limitations are removed, Google Wave is a curious and restricted glimpse into the future of communication via the Internet.
Here is an image I captured from about 1/4 of an open Google Wave window:
You will note that I have 16 additional invitations to give, so let me know if you want to play, too.