The problem with only doing 2 is that then the others will grow in, and when they don't have something to stop against (ie the two teeth you had removed) they'll keep growing, and the only way to stop this is to have special wire brace thingies put int. Trust me from experience, that wire brace thingie *sucks*. I had three second molars and one wisdom tooth removed because of a severe infection and then my wisdom teeth were allowed to grow in to where the second molars were (so I'm still 75% wise! Woohoo!), but for the several years it took all of that to happen I had a little mini brace between my one remaining second molar and the tooth next to it to keep it from growing and falling out, and it was really lame.