The features added include most all of the latest ones now found on the new PEN E-PL7. It's not often that you can apply these types of upgrades to a camera that's nearly a year old.
Besides some improvements such as speeding up it's EVF display, more and smaller AF points, and improved focus peaking, there are a lot of new in-camera creative possibilities available such as using Keystone Correction to straighten the lines of a wreck, or maybe stalks of kelp, while shooting with a fisheye lens - right on the camera back. Same with it's Live Composite Tool; allowing for multiple exposures to be made creatively without post-processing. Other cool effects like Partial Color are now available, allowing you to shoot a brightly colored subject against a black and white background.
Do you like HDR? This popular technique of shooting and overlaying multiple varying exposures (now with exposure compensation) can be set-up and shot right on the camera. Using a high-frame rate, these HDR composites can be previewed on the camera display and then saved into RAW for further manipulation later.

If you have one of these great Olympus micro-four thirds cameras, getting this free E-M1 firmware update is a no-brainer. It is easily downloaded onto a computer, then uploaded to the camera with the mini-usb cable included with the camera.
So enjoy this cool new present from Olympus and think creatively underwater, you might be surprised!
More information on the OM-D EM1 can be found here. You can download the updater here.
Here's a complete list of new features and changes:
8 New Functions:
- Keystone Compensation (Digital Shift)
- Tethered Shooting System (OLYMPUS capture)
- Live Composite
- Zoom In/Out and Layout have been added to Photo Story. Save (complete partway through), Temporary Save, and Resume functions have been added to Photo Story mode
- New Art Filters: Vintage and Partial color
- Old Film Effect in video recording
- The Aperture Lock function has been added to Aperture Preview
- The Panning Shot shooting mode has been added to SCN mode
16 Operability Improvements:
- Image display time lag in the Electronic Viewfiner has been improved to 16 msec (frame rate setting is high speed)
- Multiple simultaneous settings now available in Live Guide
- Exposure compensation (±3 EV) is now available in HDR 1/HDR2 shooting
- A function has been added to cancel Color Creator and return to the original Picture Mode by pressing the MENU button when using Color Creator function.
- Movie Tele-converter can now be used simultaneously when Art Filter is set to Picture Mode.
- AF function for each frame was added to Custom Self Timer. In Drive Mode's Custom Self Timer settings, you can now press the INFO button to change settings.
- MF Assist is now supported in magnified frame position.
- 3x has been added to high resolution magnified Live View.
- The Peaking display frame rate has been improved.
- Electronic zoom speed setting function was added. An icon appears on the LCD monitor when using an Olympus electronic zoom lens.
- When the arrow pad is set to Direct function, the Underwater/Underwater macro functions can be used with the left and down button on the arrow pad.
- Double tap is now supported in touch operations on the Super Control Panel.
- The level gauge and histogram can now be displayed during magnified frame display. The Touch Off icon was added to magnified frame display.
- A function was added so that shooting information recorded in HDR1/HDR2 can be viewed in the playback screen.
- Information on composited number of shots for images recorded with Live Composite was added (Can be checked in Olympus Viewer3).
- When the BKT button is held down, the BKT menu now appears.