Denver had a really interesting discussion about this in the past year, about what drives the feeling of player immersion. Our community here discovered that we have a lot of players whose sense of immersion is driven by character appearance, costuming and makeup. Denver has really great effort and detail in those areas, which is awesome! Now I understand why, since so many of our players seem to list that as the #1 factor in what drives their sense of "really being there." We discovered that unexpected anachronisms (by which I exclude eyeglasses, but include modern costume elements, or drinking out of plastic tavern cups, that sort of thing) can have an immediate detrimental effect on our local players' feeling of immersion.
I feel a bit like I'm the outlier locally. While I can certainly appreciate good character appearance, it affects my personal immersion not at all. Physical atmosphere is what drives that sense for me -- lighting, sound, overall mood. I could stand in a room of beautifully decorated cosplayers... under fluorescent lights, and hear the dishwasher running the background, and I am OUT creatively! OTOH, I find that a little goes a long way for me in terms of effort at covering up the anachronisms of the surroundings, adding a little mood lighting, and if there is music (recorded or live) or sound effects of some sort -- dude, even better!
I like to make my contribution to this with making sure I have a good atmosphere in my own cabin at events. I may not be able to control the setting of the whole campsite, but if I have at least one spot that I know I can rely on to be a great backdrop for the scene, that helps me tremendously with my own feeling of "really being there."
Trace