One of those is the concept of the Fourth Wall in gaming. Part of the discussion turned to subtlety and transparency of things going on in the game. One very skilled and notable GM mentioned that he likes to keep things pretty opaque, because the "A-HA!" moments are a real thrill for all involved. However, a few people expressed that they'd had great success with making things more transparent and trusting that the players will maintain a Fourth Wall, i.e., keep their player knowledge separate from their character knowledge and play their characters "correctly" based on the knowledge that they would really know.
If you are going to do this, you miss out on some opportunities for surprise, tension, and whatnot, but at the same time, you gain different opportunities. One of the most notable techniques for any author of a book or screenplay who wants to develop tension is to create a gap between what the character knows and what the viewer (or reader) knows. Because the viewer or reader knows that something terrible is coming, when the character stumbles into it, blissfully ignorant, it creates a strong sense of tension. John Carpenter was famous for doing this in the first Halloween movie, for example... allowing the camera to pan over to where you could see Michael Myers standing there with a knife, while the unfortunate soon to be victim wanders about doing nothing to prevent it.
In spite of the fact that I hadn't really intellectually grasped that simple concept, I clearly had intuitively done so, because I'd done something similar in a crude way. Many TV shows with a horror vibe, like X-Files or Supernatural tend to start each episode off with a character who gets killed prior to the opening credits. I actually did this once in a campaign; the players had all made their characters, but rather than start playing with them right away, I gave them some temporary pregens. They I proceeded to kill them with a supernatural evil NPC that had very distinctive physical features. What the actual player characters later met this NPC, it worked wonders on the players themselves.
But those kinds of techniques only work with players who are willing to maintain the fiction of the Fourth Wall. As players, they're an interactive audience, but they certainly are not the characters themselves on the stage, and they need to keep their player and character knowledge discrete. Luckily, I've got players like that, both in my online games, and in my games at home when I run (we're starting another D&D campaign right now, where I'll be a player. That'll run at least for several months. Maybe I'll put a bid in to run again after that.)
Which brings me to my next thought. I meant this as a throwaway line, and I wasn't even sure how completely serious I was about it, but someone in the chat seemed to think that it sounded at least a little bit significant, and preserved it for posterity. I'm not necessarily interested in developing more breadth as a gamemaster; rather I'd like to continue to play with other folks who are already compatible with my preferred playstyle and develop more depth to that style. Make it the best iteration of that playstyle that I can. Do what I already do well even better, and not worry about what I'm not doing. Not only can one person not do it all, but there shouldn't be any reason why we feel the need to.