The idea of finding one person to be everything in your life, including a best friend, a spouse, a parent to your children, a sexual partner.. And then to have cultural, religious, spiritual, economic compatibility is too idealistic in today's society where everyone is a strong independent "individual" and is celebrated as such.
I, personally, don't see a point in being married. But I don't want to really have a family either. Marriage doesn't determine commitment. Its really just a tradition. I'm not trying to say marriage is bad, but its kinda pointless, in my opinion. A person can have a family without marriage. I can see its importance in cultures around the world, and it clearly isn't going anywhere soon.
Marriage, and the family unit, are and always have been the absolute foundation of society. A husband and wife are like a proton and neutron, with the child serving as the electron. Just as in physics, without this fundamental order, all of reality would fall apart. Therefore, marriage is of the utmost importance.
Marriage is not outdated, nor is it an impractical idea. However, as mentioned in the earlier comments, it serves as legal protection for husband and wife. This same type of idea and concept ought to continue but the rules of who can marry who should be reconsidered. Who are we to tell someone who they can and cannot love? Same-sex couples would like the same legal protection as the "traditional" married couples.
The purpose for marriage is purely legal--it allows the state and the federal government to extend legal protection and financial assistance to partners. However, the fact that it is considered only between a man and a woman is what is causing problems. The definition needs to be updated in order to reflect modern partnerships and allow protection to everyone.
Marriage itself is not outdated or impractical, but the definition of it some cling to with such fanaticism is. It's evolved into something new, something that all that desire to be a part of it and experience it should be allowed to be able to. It needs to embrace this evolution, not be dismissed as outdated.