The problem with chopping too much right off the bat is you severely hinder your chances at getting a few early wonders since you've already spent your forests. If you're playing an industrious civ, you also will get 50% more hammers for chopping forests for wonder purposes than you will for settler production. Combine that with the fact that worker and settler chopping right off the bat is a lot of potential population lost, so even less production from your capital, and your chances at getting both the Oracle and Pyramids is lost. The Oracle rockets you a minimum of 15 turns ahead, and depending upon how good your situation is for food production, the Pyramids rocket you a lot more turns than that over the course of the game. They are without a question the two most game-impacting wonders. 90% of the time my opening strategy is completely based upon maximizing my chances to get both in order to overcome the massive opening lead the AI gets from its extra units. With all that said, one of the great things about Civ4 is that there is no one-size-fits-all perfect build queue that works every time; you have to be able to do the calculations to get the optimums. Sometimes chopping is the only way to get a settler at at the right time; other games where I have a lot of food production from fish and farms, I'd rather use high food production to crank out that settler and save the forests to help me get Oracle and Pyramids.