My .02

I think compatability is less about being exactly the same and more about being supportive of each other. Shandy and I have very different habits and pastimes. I don't scrapbook and she isn't a football fanatic. However, I'm happy that she enjoys scrapbooking and photography and I like looking at what she has created. Likewise, she supports my juvenile obsession with Boise State and shares me with my idiot friends.
It is, however, important to have something you both like to do. Shandy and I have certain TV shows that we like to watch together. We read the same books, sometimes. We try to have date night as often as possible and sometimes that means we have to just have an at-home date.
As a couple, it's healthy to have away time with your friends. For us, it's having a girl's night out once or twice a month, and my football games. On the other hand, we have known some couples that are always away from each other, doing their own thing, and I don't think that's too healthy.
It's all about supporting each other, loving each other for your quirks, and enjoying the differences that you have. Variety is the spice of life.