The main reason for bill 101 right now is to help people who only speak french (pretty common among those who only spoke english at their school 30 years ago and those who went to school before the mendatory english classes) to buy stuff in diverse shops. It requires all products sold here to have all the information on their package in at least french, or else its illegal to be sold in Quebec. Also, whenever you are served by someone in a public place or a shop, he is obligated by law to serve you in french if you understand french.
While I do understand we have to protect our french culture, since it makes us unique. I have to say though that I do not understand the reason to restrict the access to college in the english language. I have to say, if someone wants to go in an english college, even though he did high-school in french, which should you not let him do so? The guy passed his french exams in high-school, which means that he knows french pretty damn well, I am sure he will not lose it if he goes to CEGEP in english due to the fact that almost everything outside his college is in french.