The first forum was called "What Makes a Good Actor Great?" , with Sandra Bates, Zika Nester, John McCallum, Doug Anderson, David Field and Garry Maddox. Some of the answers (to the title question) they came up with were;
~ "a wonderful stillness"
~ "a way of drawing everyone in, drawing it all together"
~ "warmth, giving, willingness to be always sharing with the other actors and with the audience"
~ "being totally unselfish"
~ "generosity of spirit"
~ "making bold, courageous, brave choices"
Each person spoke about what they considered to be a truly great performance - David Field spoke of seeing a play once and that "something affected me beyond anything technical, beyond my appreciation of the acting." (paraphrased a bit) Doug Anderson spoke of a moment in a pre-rehearsal workshop when an actress shared a story with the group, saying everytime he even thinks about it, his hairs stand on end and he gets chills with the power of the way that story-telling affected him.
They spoke a little about intuition, and it's vital importance. Zika said "technique is only there for when intuition fails you, when your senses go blank". I loved that. I personally always seem to forget things I've learned about technique - I find it really hard to consciously incorporate "training" into my interpretation and preparation - so this was very validating to me, that it's okay to rely on your innate sense of the character, your emotions, the moment you're in, and to keep all the technique and "rules" way back in the back of your mind.
Another key thing Zika said was "Allow. The operative word in acting is to let things happen. Allow the subconscious to come out".
Something else that resonated with me was to be generous in your actin, to support the other actors around you. One panelist told the story of a director in a casting one day. He called two actors in first, had them read the parts etc, then as he was finishing with them he asked his assistant to "go get the next two". The assistant only found one person outside and came back in saying "there's only one here", so the director quickly grabbed one of the first actors and asked if he could stay a while just to help read with the next person. He did that with every person - he had only booked one person at a time and so every time he kept back the last person to "help", and then only paid attention to them when they were there as helper. He knew that most actors do their best work when they're not focussed on their own performance, but trying their best to support someone else.
David Field reiterated this and added that when you're a supporting actor, SUPPORT. Be focussed on everyone else, LISTEN to them and respond accordingly. He said "if you're in a film, and you have 5 scenes, and the other guy has 35, well you know it's his story, not yours". So you do your role without any thought of your own ego. You're there to be a supporting part of the story. Sandra Bates added that when everyone is truly supporting each other's performance - "everyone will look better because they're all making each other look better".
Then someone else added "Do it for the other person. Try to think as if the other person's needs are greater than your own."
David Field made the comment (above) about making brave choices in response to a question about the impact the director has on an the "greatness" of an actor's performance. His opinion was that if you're truly doing a good job, the director can't make it crap, and vice-versa (this is very much paraphrased!). He said that acting is all about *choices*. When you approach a role, you make a [bold, brave, courageous] choice about how you will do it, and you stick with it; then you see what the director makes of it. If they don't like it they can offer helpful criticism, but hey, they might just love it and it might just be exactly right.
In amongst all of that, a couple of the panelists (particularly John McCallum I think) admitted that there is some kind of "x-factor" in great actors - something that makes them jump out at you and glues you to their face and actions. It was also conceded that luck sometimes has a lot to do with it.
In summary, I think the general consensus was that generosity, sharp intuition, unselfishness, some luck, and some undefinable aura/spirit/inspiration... are what make a good actor great.