Well, it certainly depends on your own situation, but in my experience, being married was a true validation of our commitment to each other. There were issues with my in-laws and the wedding ceremony was very important knowing that not only were my parents and his parents present and witnesses, but no one discouraged us at the event. Afterwards, I felt more at ease and was able to relax more with my now-husband. I have been married for just a little over a year and I know that that feeling of security increases more with time. I suppose on the practical side, it is the fact that I can have silly banter with him and not feel insecure that an argument would lead to separation. In fact, things that would have made me quite insecure when we were first together (i.e. thinking of his ex) can now actually make me laugh or at least seem much less important in the scheme of things. I actually feel kind of amused when I can have a bit of a go at him about picking up his socks; it is all much more in jest now, although I do realise that understanding each other's moods and insecurities on a deeper level means not exploiting those things. Also, it seems like the longer we have been with each other, the more often we say the same things or are able to finish each other's sentences.
The main thing I can think of is feeling more appreciation towards my husband and simultaneously knowing I do not make as much of an effort to express these feelings. (Maybe I will, though!)