I've been playing around a bit with Eyejot, a Web site that allows you to send video messages to anyone else with an email address. Now this may not sound particularly revolutionary, but it's all Flash-based with nothing to install, and should work on pretty much any machine. It worked very easily with the built-in iSight camera on my iMac, for example. You can watch your video before you send it, and it's all quick and painless.
So why would you want to send a video instead of text email? Well, it's quicker, and I can see occasions where it's more efficient to blither-on for a few seconds than to send an email. It's all free anyway, so why not give it a go and see what you think? It's one of those ideas that might just take off...