It's not ready yet, for casual use.
I have experimented with transferring various image and video files to device, but didn't get useful results for video. All media files tested worked perfectly on both Android and desktop Ubuntu.
See also: Installing Ubuntu on the Nexus7 > Known Issues
excerpt:
- Rotation doesn't work when the tablet is physically rotated
- Difficult to scroll in Unity
- No way to right click
- Suspend from power menu (button press) does not work
- Webcam doesn't work
- Bluetooth not yet working
- Sometimes 'button 1' gets stuck down
- Shutdown is slow, taking 10-15 seconds
- Onboard onscreen keyboard doesn't always show when it should
- On screen keyboard doesn't re-position in order to see input