The Scottish Play

"...all our yesterdays have lighted fools
The way to dusty death. Out, out, brief candle!
Life's but a walking shadow, a poor player,
That struts and frets his hour upon the stage,
And then is heard no more."
-Macbeth Act V, scene v
Okay, that is a depressing way to start this off, but this is the book wraith after all.
Before we get to the actual play itself, I thought it might be interesting to have a brief discussion as to the theatrical superstitions as to why it is considered bad luck to mention this play by name in a theatre. Any thespians out there?