Goldie Hawn and Kurt Russell are one famous example of a common law marriage. I'm not sure what the law is in California now (or even back then), but I have read something to the effect that since they've been together 20 years or something, maybe 30 now for all I know (or have they broken up? who knows? I don't pay close enough attention)--but anyway, what I read was that they'd been together for so long the state considered them as good as married.
Pursuing relationships with the opposite sex seem to be generally degrading among many adult Americans.
I'm not so sure I believe that. I think *serious* relationships with the opposite sex tend to be delayed for education, but it's still sought out in equal numbers later in life, I think. Just with different proportions for long-term non-cohabiting relationships, cohabitation, and marriage. (My sister, for example, dated my brother-in-law for five years before they got married, and they never lived together. They "delayed" marriage for their educations at different universities ("delayed" in quotes, because they got married at 24 and 23, respectively, so certainly at a relatively young age for people nowadays who aren't Mormons, and about average for Mormons.)
I have seen this pattern many times for friends across the country, the most common reason for long engagements or courtships being the cost of the wedding. When weddings become $20,000, $50,000 or even hundreds of thousand dollar affairs, it takes a long time to save up if you're paying for it yourself.
That's just anecdotal, of course, but I'd love to see the cost of weddings themselves factored into a study like this.
(Which makes me grateful I'm Mormon, because at least if I get married in the temple I won't have to pay for the cost of the church, the officiator, and the decorations for the ceremony. Receptions can vary widely, of course, but that's beside the point. Though, did you know that in the state of Washington, your marriage isn't valid unless you pay the officiator? Makes me wonder how they deal with that at the temple. I keep forgetting to ask, but it makes me curious. Not that I'm in any danger of needing that information for practical purposes.)