Woozlet: DP and I have discussed it so many times, whether we "ought" to get married for practical purposes even though neither of us sees it as much of a priority, and we've always decided not to (instead sorting out our wills and finances properly, etc). So I don't think he would surprise me and propose, because he knows it's not remotely a secret desire of mine or anything like that.
If he did still propose for some reason, though ... well, we'd talk it all over again, I guess!
We have been together 13 years and I love him so deeply and am absolutely committed to him I know he feels the same. But our families are far-flung, with many rifts and problems, and I grew up witnessing the horrible effects of my parents' very bitter divorce, which they both literally never stopped going on about for years (I was their only DC and remaining connection, so they took anger at each other out on me), and for these and other reasons, generally speaking the notion of a wedding has never interested me, even as a fantasy or whatever. I just never saw it as the only true measure of committment; I think marriage is great for some people, but it didn't ever attract me. I always dreamed of finding someone I could truly love for my whole life, and I found him but getting married has never seemed important or especially desirable to me. Luckily DP completely gets this and it makes no difference to him.
I'm not saying we will never do it. I don't hate the idea; but nor do I feel it's remotely necessary to prove our committment. The happiest family I knew growing up were a couple of lads whose parents had never married but had been 20+ yrs together, so I guess they were another early model to me that indicated marriage wasn't necessary to prove anything about your status as a strong couple or family.
Seeker, Lawks and others give me hope that Mumsnet is a place where most people get this. I have to say I've been quite upset by some comments about cohabiting relationships on other MN threads recently, though.