The Settlers of Catan is a magnificent game, in my opinion it is one of the greatest gateway games in existence. However the game does have some inherent flaws. The perceived randomness caused by the dice-generated resources is one of them.

Mechanics & Game Play:
Playing The Settlers of Catan with the Event Cards is mechanically no different to playing a game with the dice. Each turn random tiles generate resources, but instead of rolling dice in this variant you draw the top card of the deck. This card will have a number on it. The number corresponds to a possible roll on 2D6. Each number is 'statistically accurate/correct' within the deck. Some cards also have events on them that add a little bit more spice to the game.

How Does This Correct The Randomness (AKA The Mathematics):
Statistically speaking, each die roll is an independent event. That means that every time the die is rolled, each number has the same probability of being rolled. On the other hand, in a deck of cards each draw is a dependant event (As if a card has been drawn, it is impossible to draw it again until it is replaced and the deck is re-shuffled). So what the Event Deck does is bring the distribution of the numbers rolled closer towards 'pure probability'. In addition to the 36 cards there is also a 'New Year' card that returns all cards to the deck and re-shuffles. The Event Cards suggest that you put the New Year as the 6th-last card, though I personally suggest that you shuffle it into the deck. The New Year card is designed to stop the game being a pure maths-fest (By adding a little bit of irregularity to the Bell-Curve)

The Events:
About half of the cards in the deck have events on them. Many of the events give a resource for meeting a specific critereia (Longest Road, Largest Army, Most Harbours). There are events that 'partially destroy' sections of road, forcing the players to repair the road (1 Brick, 1 Wood) before any new roads can be built. The 'Robber Flees' event sends the robber back to the dessert. Some of the events are quite powerful, enough to perhaps force a change on already developed strategy.

Is It A Good Thing?
Personally, I like the Event Cards as an occasional change-of-pace. I certainly won’t use them in every game, but I will more than likely use them in about half of my games. The cards also add a balance factor, as many of the events help to give the trailers a boost. But mostly, the cards give the 'dice-whiners' much less room to affect the mood of the game (as well as forcing those who rely on the luck of the dice to win a game purely on skill). However, if the dice do not bother you too much, then I don't think that I'd bother.