Facebook has announced that developers will soon be given the power to email users via their applications. In the same way that you get an email when you're tagged in a photo, you may soon get a message to tell you that someone's recruited you into their mafia family.
Don't worry - you won't get spammed too much - you have to explicitly grant permission to an application before it's able to send you emails. It'll empower developers to send receipts for purchases, newsletters or action notifications. Developers will have to include an "unsubscribe" link, for those irritated by the messages.
If you're not comfortable handing over your work address to Farmville, you also have the option of sending a proxied version of that address - a unique string of digits and numbers - and Facebook will forward any mail received in that box to your regular email address.
The obvious conclusion of all of this is that Facebook is making it easier to interact with the site from places where it's banned - offices, schools, etc. Sure, it might lose a few page views, but having people click straight back on when they get home is far more useful to the site in the long run.
Despite the unsubscribe option, there's been considerable backlash to previous changes that Facebook has made. It remains to be seen whether the same thing will happen following this announcement.