It is true that apparitions fall under a category called "private revelation", which is not required for us to believe in as part of the Catholic Faith. So La Salette, Lourdes, Fatima, Medjugorje, etc. are all considered private revelation.
But, many incredible graces come to those who believe and follow these private revelations. We have all heard stories of dramatic healings of mind, body, and spirit in all of these major Marian apparition sites. Medjugorje is no exception, and I have personally witnessed many incredible miracles that have come about as a result of the special graces given in Medjugorje. Our Lady has said many times in Medjugorje that we are living in "A Time of Grace". Our Lady asks us to take advantage of this grace to change our lives back to lives that will lead us to heaven rather than eternal damnation. As much as modern theologians and preachers of many denominations try to white wash this reality, there are only two places we can ultimately go, heaven or hell. Satan has done a very good job at making people believe he does not exist. We must put on the "Full armor of God" as St. Paul says if we are to survive satans attacks.
It is incredible to imagine that Jesus loves us so much that He has sent His mother to earth as early as the 1300's to warn us, and implore us to change. Historically we have done a poor job of listening and responding.
At this time (July 2006), Ivan, Vicka, and Marija have each received 9 secrets and still receive daily apparitions from Our Lady. Ivanka, Mirjana and Jakov have received all 10 secrets and will see Our Lady once per year for the rest of their lives.
There was a question asked of Our Lady in October 1981 which was: Are all religions the same? Our Lady answered: "Members of all faiths are equal before God. God rules over each faith just like a sovereign over his kingdom. In the world, all religions are not the same because all people have not complied with the commandments of God. They reject and disparage them."