The Cubs' inability to win a single WS since 1909 is one of the strangest sports "things" out there. Major market, popular franchise, many very good players, etc. The big problem the Cubs have had is that the Cubs as lovable losers still sell out a lot of their games and still make gobs of money, so there hasn't been the same incentive to win as other franchises have (most other franchises need to win to garner fan interest).
That said, the Cubs have fielded some really good teams -- the Sandberg/Dawson/Grace/Maddux teams as well as the Sammy Sosa teams and then a few more since. And these are just the recent teams. You'd think that at SOME point they'd win a WS from the mere fact that they've had 105 years to do it again. Alas, here we are. I do think the Cubs win one in the next 5-10 years. New management has brought in Theo Epstein and Joe Maddon and the franchise is making moves and building up a young core that could be good for a while. Give these young guys a year or two and the Cubs will then go out and throw truckloads of money at a few star pitchers and they'll be in the mix.