You guys need to find some funner friends
Marriage seems to be an anomaly among my friends. Many of us had our starter marriage, and don't want to go through that again. Some are in long term relationships, and don't feel the need to "prove it" to the rest of the world. Some are sowing their wild oats, many are working on careers first (lots of that). Then, lots of us get to be around 35, like berrettafan, and realize that having children becomes a riskier proposition, as he are dealing with. So, they decide to not have kids, and if you don't have kids, and two strong careers, and have lived together/share credit/own a home and cars, but aren't married...well, why bother getting married? If you're going to have kids, then yes, go forward with that. But, if you're going to be DINKS, then what changes really between being married or not?
That's where Sue and I seem to be right now. 35/36, pretty much have written off kids, two strong busy careers, buying a house next year, been together for 5 years, both married and divorced pretty early with no baggage from that...why bother too much about a ring at that point? It won't change our life, or the way we live it.