As Mark Hulbert noted recently, "everyone" is worrying about a "bubble" in the stock market. To wit:

"To appreciate how widespread current concern about a bubble is, consider the accompanying chart of data from Google Trends. It plots the relative frequency of Google searches based on the term 'stock market bubble.' Notice that this frequency has recently jumped to a far-higher level than at any other point over the last five years."

What Is A Bubble?