Basically when you press a chat for a few seconds you now get the two options: "Delete conversation" "View contact profile" or "Delete and exit group" "View group information"

In whatsapp, you get a third option "Mute conversation" which mutes all notifications from new messages in said chat. The messages are received as usual but you just don't get the ringtones.

Keinc has collected solutions and worarounds for some of the most common problems here: http://write.keinism.com/2012/08/30/...d-and-working/