Besides a new favicon and a confirmation dialog displayed when you mark all the posts as read, Google Reader now shows the published date of a post in a tooltip. Next to the snippet, Google Reader displays the date when the post was indexed by Google, not the date when it was published. Sometimes the difference between these two dates can be a single minute, but it could also be much bigger.
Google Reader also added some new keyboard shortcuts: a to add subscriptions, g+d to open the feed directory, e to email the current item. You can see the list of keyboard shortcuts by typing ? in Google Reader.