While "show, don't tell" is probably a cliche of writing, it is a true one. Tell, tell, tell, blah, blah, blah puts most readers to sleep. It has something to do with statics vs. dynamics, something I've been thinking about regarding writing. Showing is much more dynamic, while telling is more static.
Geoff Herbach did a guest post at Fiction Notes called Replace Abstractions with Concrete Detail in which he talks about how abstractions often lead to "telling" in writing, which concrete details "show."
It sounds pretty simple, and simple is a good thing.