Gonna have to play the "every situation is different" card here. My marriage has been great. I proposed about a year after we first met. We had zero problems when we were dating and never argued, not even once. We were very compatible with each other. She was unwilling to move in with me out of marriage, but she stayed over at my place enough times and there were no problems being together for longer periods of time, either. We enjoyed each others' company very much, so getting married seemed like the next logical step. It was after getting married that some problems did arise, but again, nothing too major. We rarely ever tend to argue with each other. We just celebrated our third anniversary a few weeks ago, and things are better than ever.
If we argued or fought with each other while dating, or if there seemed to be any major issues that might factor in later (cultural/political/religious/family/children/whatever), there's no way in hell I would have popped the question. Take as long as you need to decide if you want to get married or not. It's definitely not for everyone. One of my friends is more than happy being single. He doesn't want to sacrifice any of his free time dealing with someone else. I think that's kinda nuts, but I see where he is coming from. To my knowledge he has never had a girlfriend before. He's over 30 now. He's in good shape, has a good job, lives by himself and all that, plus has plenty of male and female friends, so it's not some weird social or physical issue. The guy just doesn't seem to care.
Another seems to rush into relationships too quickly. He'll date someone for a while and it will end, he'll say "fuck 'em; imma be a bachelor for a while," and then the next thing you know, he's found himself another girlfriend who is eerily similar to the last one. He's getting married to his current girlfriend early next year...I think he's been dating her for a year and a half or so, so it's about the same time frame as my wife and I getting married. But I am worried about him because he's wanted to get married to virtually every girlfriend he's had. (He actually proposed to his first girlfriend like a month after they started dating, and the girl's parents broke it off) I don't actually know this girl very well (only met her once; this friend and I never hang out anymore), but they are always all over each on Facebook and post a sickening amount of messages to each other. They seem to have similar interests so I hope things turn out wonderfully for them.