Cnet disclosed that Gmail has "released major structural code changes and is rolling them out slowly".
The older and newer versions have the same user interface and nothing differentiates them at first look although the contact manager is now easier to navigate.
However, it looks as if Gmail pre-caches messages and "saves" them on your computer so that the overall email reading experience is smoother.
The size of the editing area does not change when you shift from plain text to rich format - a welcomed change.
But the newer version actually "feels" a bit slow especially when it comes to scrolling up and down and users have reported that it is often slow at loading initially