Maybe it is my interest in science, or my disinterest in the world around me, but I'm a fan of Science-Fiction. Whether it is in print or on screen I enjoy a good story that uses (pseudo)science as a device. From the works of Roddenberry, through the likes of Doctor Who, or The Hitchhiker's Guide to the Galaxy I've escaped the mundane many-a-night. These, and so many more that I've enjoyed, are all guilty of the "Alternate Reality" device. (While Douglas Adams was at least sharp enough to make the distinguishment from "Parallel Universes")
Just in case you don't know, the idea of "Alternate Reality" (or at least one rendition thereof) is that each decision that is made one way, is also made every other way in an ever growing number of forking alternate realities. For example, your decision to read this paragraph or not will result in the creation of an alternate reality in which you made the opposite decision. Thus it is for ever decision you make, and every decision everyone makes.
That's a lot of realities.
All these "realities" gives the writers many, many options into which to take their characters. This makes for a very flexible device for any science fiction author.
My first problem with this device is that my very decision to go to an alternate reality should create two more alternate realities: a version of my home reality from which I never left and a version of my destination reality to which I never went.
What is the result of all the decisions I make in the version of reality that I am visiting? (my second problem) Do they create forks in the reality I belong to, the one I am in, or both?
My third problem is (or should I say are) all the decisions made in my home reality while I am gone, or to be more precise, all the subsequent alternate realities created by those decisions. Which one do I go home to?
I still enjoy my science fiction, but until I see a story that adequately handles these problems, I will view the "Alternate Realities" device as second rate -- a cheap trick.