Question for the audience

An interesting question emerged during a discussion with some buddies/co-workers/peers/whatever-you-want-to-call-them today:

"Which conferences have you attended in the past that you thought was really good, and why? Which sessions were your favorites, and why? What made them that way?"
(The root of the question was simple at its heart: What makes a good conference session?)

Yes, this is somewhat selfish, since the new conference season is amping up, and obviously I'd like to make sure my sessions are ones that people find interesting and recommend to others, but the question actually stemmed from an unrelated discussion to that. I promise. :-)