Good how viewing the message shows the sender(/recipient ?) image (from Contacts) when reading the message.
Real nice if the message lists (Smart Inbox, Inbox, Sent, etc.) could have a configurable option to show the same image (maybe superimpose the "Read tick" smaller to bottom right). It would need to be a settings option as some people would not like it (limited screen space, processing power, whatever).
Doesn't allow you to do anything new but for some/many the quality of the UI is an important aspect to selecting software.
