Interface Misc
Quick Options
Many of the buttons have options that have always been assigned to them. For instance, when you render there are render options that correlate with it. Now if you Shift click many of the buttons that have options, the Options dialog will come up with the correlating tab selected for the options for that button.

Render Options
Shift clicking the Render Mode button will bring up the Rendering Options.

Lathe Options
Another example would be shift clicking the Lathe button to bring up the Modeling Options, which contains the Lathe Cross Section option.
First and Last Frame Buttons can be added from Customize Dialog

First and Last Frame Buttons
First frame and last frame buttons have been added to the list of buttons that can be added to a toolbar. Simply drag the buttons from the Customize dialog to the desired toolbar if you wish to use them.
Draw Particles and Hair

Draw Particles / Hair
Particles and Hair can now be turned "ON" and "OFF" in the Render Options. This is useful for doing render tests and you don't want the added expense of calculating the particles or hair on your model.