Multiple media outlets are reporting that Facebook and MySpace have sent out invitations to a joint announcement webcast to take place today at 12pm US Pacific time (8pm UK time). The invitation specifies that MySpace CEO Mike Jones and Facebook vice president of partnerships and platform marketing Dan Rose will be on hand to announce, well, something.
Reading between the lines, the fact that Facebook CEO Mark Zuckerberg won't be on-hand pretty much rules out any possibility of a merger between the two companies. What does seem possible, though, is that MySpace could be planning to adopt the Facebook apps platform - a hypothesis echoed by Mashable - or perhaps somerthing ad-related.
In either case, we'll find out soon enough.