Facebook announcing email service Nov 15th?

The people over at TheNextWeb received an invite from Facebook for an announcement: it had them puzzled because recently the announcements of mobile, Places and Deals have already been done. Their wild guess is that Facebook might finally be announcing an email service, which was rumored to be in the works in February under the name of Project Titan.
The guess is based on the looks of the invite, its design is like an airmail envelope and has the messages icon from Facebook on half of the page:

If this guess turns out to be correct and Facebook offers all its 520 million members an email address this could put them ahead of Yahoo, GMail and Hotmail in terms of total amount of email members. Also, this could be a new platform for Facebook to put advertising on.