Late tomorrow, Facebook's going to make an announcement of some sort, and if rumors are correct, an important product will launch. Facebook is supposed to unveil a geolocation service at its headquarters. This isn't a sure thing; official messages on the subject have been very vague, just providing a time (4:30 PM PDT) and an address (1601 California Avenue in Palo Alto), and saying that unspecified "Facebook executives" will be on hand.