One of the more annoying thing that can turn people off virtual worlds is difficulty moving around, especially when the user gets their avatar stuck on the geometry of the world.
It is really a matter of environment design. Don't make tight areas where users can get trapped. When making objects with lot of little details try to make it phantom but then add an invisible, simplified object to provide a collision object. Think about lines of sight that allows users to easily see notable landmarks and create distinctive zones (architecture, colour, etc) that allow users to keep a sense of location.
These are all common sense guide lines, but it is easy to forget them when designing an area.