The new firmware was actually released earlier this week but there was a bug with audio recording in the creative modes. Today, they did a minor fix with the release of firmware version v2.0.4.

Here are the changes:

The Version 2.0.4 firmware includes the movie function enhancements listed in items 1 through 5 below, and also incorporates the correction listed in item 6.

Adds or changes the following movie frame rates.

NTSC:
1920×1080 : 30 fps (changed – actual 29.97 fps)
1920×1080 : 24 fps (added – actual 23.976 fps)
640×480 : 30 fps (changed – actual 29.97 fps)
PAL:
1920×1080 : 25 fps (added – actual 25.0 fps)
1920×1080 : 24 fps (added – actual 23.976 fps)
640×480 : 25 fps (added – actual 25.0 fps)

Adds a function for manually adjusting the sound recording level (64 levels).
Adds a histogram display (brightness or RGB) for shooting movies in manual exposure.
Adds shutter-priority AE mode (Tv) and aperture-priority AE (Av) mode to the exposure modes for shooting movies.
Changes the audio sampling frequency from 44.1 KHz to 48 KHz.
Fixes a phenomenon where communication between the camera and the attached lens is sometimes interrupted after manual sensor cleaning. (This phenomenon only affects units with Firmware Version 1.2.4.)

How to update your firmware:
Updating your firmware is really simple. However, I suggest you follow the official procedure if you have never done it before.

Here’s a simple step by step recap.
Step 1. Format your compact flash card in the 5D mark II.
Step 2. Remove the CF card stick it in your computer’s memory card reader.
Step 3. Open up the CF card in your browser. You will see 2 folders.
Step 4. Download the new firmware. Extract it and copy to the root directory of your CF Card.
Step 5. Place the CF card back in the 5D.
Step 6. Make sure your battery is charged. Important!
Step 7. Navigate to firmware and hit set.
Step 8. The camera should find the new firmware and give you the option to update it.
Step 9. Hit OK, and then don’t touch any buttons on the camera. You will see a progress bar as it goes through the update process which should only take a minute.
Step 10. Format your card again once it has completed. Happy Shooting!

Press Release:

LONDON, UK, 27th May 2009: Canon announced today it will release a firmware update for the EOS 5D Mark II allowing users to manually control exposure when shooting video. The new firmware will be available for download from 2 June 2009 on Canon Europe’s support web site.
Following the launch of the EOS 5D Mark II in September 2008, Canon’s Research and Development team has listened closely to customer feedback to develop additions to the camera’s movie recording functionality.

Allowing EOS 5D Mark II owners to achieve even more stunning video results with the camera, the firmware update will include the following manual controls when shooting video:

Full aperture selection
ISO speed: Auto, 100 – 6400 and H1
Shutter speed: 1/30th – 1/4000th second

The EOS 5D Mark II integrates full HD movie capability into a high-end 21.1 Megapixel camera; opening a multitude of new possibilities for photojournalists and news photographers. Since its launch the camera has proved its appeal to professionals working in diverse fields, from studio and wedding to nature and travel. Now, following customer feedback, Canon has improved functionality for professional video users, further unleashing the potential of the EOS 5D Mark II for cinematographers and photographers alike.