In the TNG Technical Manual, I believe it said that the floors move for each individual user, an omni-directional conveyor belt basically - so that no matter how much you walk, you'd never hit the walls. The holo-matrix projects the other people in the holodeck with you as part of the simulation (to your perspective) so that they can seem far away when they're not. Something like that. I find it interesting so many people are turned off that the holo-simulations are "too real" (not glitchy enough). I've personally never had any issues with that - hadn't even considered it. I DO however think that "holo-addiction" would be unlikely, simply because of lack of access. Even assuming that a Galaxy Class starship had.. even 20 separate holodecks, with over 1000 crew members, that's a lot of wait time for your turn. The shows always implied that everyone (including low-level officers and civilians) had easy access to the holodecks and could spend hours every day to recreate, but that just wouldn't be feasible. Even in the 24th Century Federation, there are some limitations.