I have just finished a video production for BMI Healthcare using a portable green screen, 2 metres by 1.5 metres. I filmed 7 people against this, in a meeting room at a conference center in London, where all of the interviewees were all present on that day. Green screen is an effective way to shoot interviews and enabled me to put the people in front of a unifying background. Using a selection of soft lights I was able to create a smooth even light on the green screen which made keying very easy. A cameraman I work with many years ago gave me a great tip when lighting for green screen, and that was to use green gel on the lights that you are lighting the green screen with, I have always done so ever since. I also used two backlights, normally I only use one, to give the subject more separation. In the edit I had to drop the intensity of the graphic background down and also use a Gaussian blur to make the subject more prominent.
The client was very please with the result and will be sending out copies to all 14,000 staff. Another example of how effective video is, when trying to communicate with many people in a large organisation