Typically, low quality playback only occurs during the first moments of the stream; low quality playback is the result of slow Internet connection speed. In order to comply with Mobile Data requirements of 3G access, we must first encode the movies at a super small 64kbps version which is of horrible quality. When you start watching a movie, the Android operating system will detect the speed of your connection, select the highest quality of playback that it can support and play the entire movie at that rate.
To ensure the highest quality streaming available, you should have the "ENABLE HD STREAMS" option checked. To do this, select "SETTINGS" from the main menu, and then check the box labeled "ENABLE HD STREAMS". Checking this will ensure your device is always using the highest quality playback possible, but may cause erratic playback on slower Android devices.