So MLB is adding a second wildcard team for each league, and the two wild cards will have a one-game playoff.
Let's imagine what this would have meant for the 2011 pennant races.
2011 National League:
The Phillies, Brewers, and Diamondbacks still win their divisions, obviously. The Cardinals still win one of the wild cards, and the Braves win the second one. The last-day drama between those two teams would have been eliminated, but the Giants would have been in it a little longer, finishing up just a few games out of the second wild card.
The Braves would then have visited the Cardinals for the one-game playoff, with the winner going on to play the Phillies in the divisional round.
2011 American League:
The Yankees, Tigers, and Rangers still win their divisions and the Rays still win one of the wild cards. The Red Sox win the other wild card, eliminating all that drama as well. The Angels finished 4 games out of the second wild card.
The Red Sox would then have visited the Rays for the one-game playoff, and the winner would go on to play Texas since both wild card teams are from the AL East and can't play the Yankees.
So, 2011 would have been a lot less interesting, but we already know that it was a historically incredible season.
But, check out how 2010 would have looked with the two-wildcard system.
2010 National League:
The Phillies, Reds, and Giants still win their divisions and the Braves win the wild card. The Padres, who finished just 2 games behind the Giants for the NL West title, win the second wild card.
2010 American League:
Here's where it gets really interesting. The Rays won the AL East while the Yankees won the AL Wild Card. The Yankees, however, were just 1 game out, and you'd better believe they'd greatly prefer to win the division and avoid the 1-game wild card playoff. In the actual 2010 race, the Rays and Yanks were well ahead and there was no tension over either the AL East division or the wild card. This would have really changed things. Then there would have been a race for the second wild card between the Red Sox and the White Sox.
If the Red Sox won the second wild card, then they would have played the Yankees in the one-game playoff and the winner would then have played the Twins. If the White Sox won the second wild card, then they would have played the Yankees, and then the Rays if they won the one-game playoff.
Anyway, the bottom line is that the new system will add some drama some years and remove some drama in other years. Overall, perhaps one or two more teams each year will be in it at the tail end of the season.