More than 80% of our communications are done using "signals" rather than words, (says paralanguage expert Dennis Tooley).
So for a start, if you have a web-cam and a G-mail account, then you can use the predefined motions set by the Gmail engineers to make or reply to your e-mails (including creating words within mails of course). I'm not quite sure even if you're a paralanguage expert, you could use this feature to create a complete set of words using hand/body motions since it is still at beta stage, but when looking at the official video, it looks promising though.
But to be honest, I won't be using this "feature" in front of my friends since in my opinion it makes me look like an idiot (aaah, the power of perception eh ;-) ). For instance, if you want to tell G-mail to send your message, then you have to imagine posting a real world mail, followed by conventional body movements, touching your lips and stuff (see the video below), but in front of a computer, this looks a bit "weird".
Still, I already like the reply to mail signal which is showing your "thumb" and if you use both of them, then it means "reply to them all" according to the designers. And to show your anger, it would be nice if they could assign something to the "middle finger" too, which is another very widely used "symbol" these days ;-).
Anyhow, it should be interesting how people react to this, but according to Google, from a more productive point of view, researches have shown by using this G-mail Motion feature, users have in fact been able to create words quite efficiently when compared with the conventional touch or typing in general (see the below picture).
|G-mail motion chart|