As a Cubs fan, I can tell you we haven't won the Series since 1908. (Don't say that was the only time, though. We won it in 1907 too.) We haven't even been there since we were cursed in 1945. We didn't even make the playoffs from 1946 through 1983. We've sucked, and when we haven't sucked we've had other things happen *coughBartmancough*. And even worse, our players can't even win when they go to other teams.
Since the Curse, only two MLB teams have won the World Series with 3 or more ex-Cubs on their teams -- the 1960 Pittsburgh Pirates and the 2001 Arizona Diamondbacks. Thus the only proven way to defeat the Factor is to score the winning runs in the bottom of the 9th in the 7th game of the World Series, and it must be against the Yankees (who swept the Cubs in two World Series in the 1930s).
The Factor has been especially powerful in the last two years, however -- in 2004, the Boston Red Sox broke their Curse by becoming the first team to come back from being down 3 games to none to win the ALCS over the Yankees 4-3, and going on to beat the Cardinals in the World Series.
Who could predict this? Ex-Cub Factor aficionados. The Yankees were set up perfectly for a historic collapse, taking no fewer than SIX Ex-Cubs on their team.
In 2005 the Factor was again powerful. Four teams - the Yankees, Cardinals, Red Sox, and Padres - had 3 or more Ex-Cubs. None of these made the World Series, and 3 of them (all but the Cardinals) lost in the first round. The Braves, who had 2, also lost in the first round, leaving the Angels (1) vs. the White Sox (1), and the Cardinals (3) vs. the Astros (1). The White Sox defeated the Astros in the Series, and the Factor held again.
Here's a list of Ex-Cubs on the rosters of the 2006 playoff teams (note: coaches, managers and the like do not count, nor do players that were only drafted by, but did not play for, the Cubs):
Los Angeles Dodgers: Greg Maddux, Nomar Garciaparra, Kenny Lofton, Ramon Martinez (4)
San Diego Padres: Todd Walker, Mark Bellhorn, Manny Alexander, Scott Williamson (4)
New York Mets: Michael Tucker, Steve Trachsel, Mike DiFelice (3)
New York Yankees: Miguel Cairo, Kyle Farnsworth (2)
Minnesota Twins: Rondell White, Phil Nevin (2)
Detroit Tigers: Neifi Perez (1)
St. Louis Cardinals: Jose Vizcaino (1)
Oakland Athletics: None (0)
Thus the Dodgers, Padres, and Mets will not win the World Series in 2006. Better luck next year, guys.
Edit: The St. Louis Cardinals, the only playoff team from the National League with fewer than 3 Ex-Cubs, won the 2006 World Series. Their opponents, the Detroit Tigers, were not cursed -- unless Neifi Perez counts as 3 Ex-Cubs by himself.
Do not taunt the Ex-Cub Factor.