Here is a (very informal, not conference-style) paper about worlds, which is something that I've been working on lately. I'm pretty excited about this stuff... Please let me know if you have any comments, suggestions, etc.
Tap, tap, tap — is this thing on?
Update: Chapter 4 of my dissertation is an improved version of this paper. It contains more examples, a formal semantics for property/field lookup in the presence of worlds, and a proper Related Work section.