While at its most basic Google Wave can be seen as a combination of instant messaging and e-mail, there is a lot more going on. New participants can be added to a wave at any time either by clicking "Add" on the wave or dragging and dropping a contact from the Contacts pane on the left to the wave.
Once a wave is in progress, users can add pictures by simply dragging them into the wave. These will progressively download, so that the thumbnails of the pictures appear instantly, while the full image is loaded in the background. Users can also conduct "quiet" conversations with one or two other participants within the actual wave, and these cannot be seen by the other participants unless you want them to.
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