For a company as quirky as Google ( GOOG), one thing is surprisingly predictable: The seasonality of its stock. Since the company went public in August 2004, October has always been a strong month for shares of Google. And a selloff at the start of the new year seems to follow like clockwork. As the bullish sentiment surrounds Google again -- shares are up nearly 20% in the last month -- the stock's trading pattern is important for investors to keep in mind. A slew of analysts have gotten in behind the stock as it ascends, citing new reasons to back the company. Although many of the reasons that the company has seen its price target get boosted are valid, investors need to realize that shares move as much with the whims of the market as they do because of fundamentals. In the meantime, October looks like it should deliver another bull run for Google. In October 2004, shares rallied 44%. They ran up 17% in 2005, and 19% in 2006. Only nine days into October 2007, shares are up 5%. Google's overall late-year run-up is even more pronounced. Starting in August and ending in January 2005, shares rallied 91%. Between August and January 2006, they rallied 51%. And they rose 32% for the same time period ending in January 2007.