You'll be able to give out your email as email@example.com.
This is widely expected to be the big announcement at Monday's Facebook event. For a lot of people, Facebook is already the first screen you go to when you go online, before email even. But if they could also be your email site, that could be huge because it would put them even further at the center of your online world, which is what every single person in that company is working towards. This could be a danger sign for Yahoo and AOL, maybe even Google. The new product is said to be deeply integrated with Microsoft Office, so it might look and act a lot like Outlook, though hopefully better.
Of course, this all depends on the product looking good and working well.