No, Facebook will install it automatically. With MySpace you had to do a separate download to get the MySpaceIM client.
I told my younger sister about Facebook's announcement today, and she didn't really care since she already had Skype to video chat with her friends.
I have Skype and Facebook both today too. I have like 8 addresses in my Skype book. I have about 200 friends in Facebook, which includes almost everyone I talk to. I don't think my setup is all that unusual.