Good tips. It's surprising how much more information you can get from just staying silent and actually not even saying "Mm Hm" or "yeah". It leaves them more time and room to elaborate.
Summarizing and asking "what do you mean by that?" or "how so?" can also help give you information you would have otherwise not have had.
I'm trying to work on retaining information better... I guess it helps when you ask questions and summarize.