Similarity in the important things is a must.
Other then that, why would you want someone who is exactly like you" booooring. But thats your choice of course.
My mother and I have a horrible relationship because we are exactly like each other. We clash on everything because we are always butting heads, not opposing heads but heads trying to fit through a door at the same time
Or perhaps fighting for which one goes first maybe. Either way, I have very negative experiences of people in my life who have been exactly like me, including boyfriends.
I think its important that we are able to learn from our partners, and share new things that each of us like. I think there is a great joy to be found as well in sacrificing yourself to do something your partner loves even if you don't care for it. Its a great life lesson and it *can* bring you closer together then if you simply loved all the same things. Healthy challenges to compromise on and overcome are not bad things, they are relationship-builders that help you maintain tip-top relationships by excercising communication and learning to enjoy just each other as people rather then for what you are doing together.
*rambles* anyway.. my personal opinion is that two people exactly the same make a pretty boring couple
But other then the fundamentals (faith, morals, etc. and other non-compromiseable fundamentals), people can pick whatever kind of partner they like.
And I don't mean people have to be opposites either.. but rather, its a completion, a balance, that you are looking for. Too similar is just as bad as too different is as well. Balance is the key
~ ~