I hope that they dont force me to use a fb login in whatsapp now!! That'll really suck.
Buying a messenger was only logical for fb...fb chat was not going to compete with the likes of whatsapp...if you cannot beat them, buy them :D
Synergies in Viber - Rakuten deal seems better as there is a minimal overlap of user base especially in terms of geography.
Now FB has another layer of data about our phone contacts..
I did a feature comparison to mobile messengers a while back. https://docs.google.com/spreadsheet/ccc?key=0AtWoXGrBr42pdDl...