Gonna make a quick straight to the point post from a scientist.
Theories are supported by mountains of evidence, facts. The word theory in science is not used the same way as one of Andy Griffith's hunches. Furthermore theories are not proven nor do they need to be. We can often times assess the usefulness of theory by its ability to predict. In this case evolutionary theory is very useful at prediction. We use theories in science to support laws, facts of life if you will.
A different subject example is planetary motion. The planets rotate about the sun and do not fall into it, this is a fact of life, a law of nature. But why? There is many theories that support this, from Newton to Lorentz.
Evolution is a fact of life, a law. Theres no way around that. It is not a belief, it is not disputable. Many, many, many (insert many more many's here.) technologies and medicines are based upon evolution. They work because evolution is a fact of life.
Evolutionary theory describes the mechanisms by which evolution occurs. The theory, supports the law. Theories are often revised, a revision does not mean they are incorrect. Revision on only adds to the predictive power of the theory. Evolutionary theory makes many correct predictions of the world, therefore we know it is fairly well describe theory, that is not to say it is all encompassing or complete. We have much to learn still about evolutionary mechanisms. This process can take centuries, as with the earlier example, it has taken us the better part of half a millennium to describe planetary motion with the accuracy we can today.
Edit: Actually you could say it has taken us the better part of 2 millennium.
To express disbelief in evolution only lets your ignorance of how the world works show.
Many creationists misuse or misunderstand science being critical of itself. Scientists are just as critical of evolutionary theory as anyone else. In this way we ensure we get our science correct. This is where evolution and creationism differ greatly. Most creationists are not critical of creation, Creationism under the lightest scientific scrutiny falls apart. For this reason, I believe, they attack evolution or feel threatened by evolution. That is why creation is a matter of faith, there is no scientific evidence to support the claims, it can only be faith to accept ideas without evidence. I am not saying this is wrong, its up to each of us to decide our beliefs.
I have noticed though, how creationists accept evolution slowly, as in waves. Once upon a time, any evolution was impossible, then that changes to "well macro evolution is not possible", which transforms into oh yeah evolution is really a tool of God, he set evolution and speciation into motion. Thats just an observation I have made, but anyway now I am ranting and I had said this would be breif