After reading through several creationism sites I have noted some of the main problems pervading them. First is they are almost always Christian, and they treat this as an absolute. So while science changes and renews itself becoming closer to truth they are always restrained by their belief on God, if anything rejects that belief they have no choice but to oppose it regardless of its validity. They often believe that because their is an inconsistency within a scientific theory that promotes atheism it somehow enforces their argument for God. An example in a very simplistic form would be "there is no empirical evidence for evolution, thus God exists."
This one they are especially guilty of, the sharpshooters fallacy. This involves making up your mind, then finding the evidence that supports it, while ignoring the evidence that contradicts it. This is done often because they make up their minds about God, then try to find evidence for his existence rather fairly interpreting the facts. This is often done with statics, which by themselves prove little. For (a fictional) example "Of the 100 highest IQ holders in the world 83 said they enjoyed alcohol, Thus alcohol improves cognitive power." The problem with this being is it is not made clear how much they drink, how often and if it was only for a certain period of their life if they have stopped. Add to this the empirical evidence of alcohol being harmful to the brain. They are also usually amateur scientists (if even scientists) which means the topics on which they criticize they do not understand very well or at all. This is mostly because they is so little credible evidence for science that supports a literal reading of the bible. The only people who belive this scientists are those who read the bible as a literal text of the universe. A prime example of their lack of knowledge on a subject being they belief that the Big Bang theory is the universe coming from nothing, when in fact it is believed today that the Big Bang theory originated from a small amount of super heated matter that has always been there.
They often intentionally of unintentional confuse terms to make accepted scientific theories seem weak. The word theory in common use means an unproven idea or a conjecture where in the scientific community it means an idea that is consistent with existing scientific knowledge that explains an event/phenomenon. In science nothing is certain nor will it ever be, with the only two things it can happen in being maths and logic. However because it cannot be proven for sure the creationists attack by saying that since it is not proven it should be taught alongside their theory. Strangely enough (especially in the U.S.A.) they try to call theories like evolution a religion to denounce it and to put it on the same plain as their beliefs. They claim it is dogmatic, requires faith and venerates people (like Darwin) as saints. The problem with this is that it is not dogmatic, as it has been revised many times leaving many of Darwin's theories obsolete (which also removes the idea of him as a patron saint). Couple this with the fact a religion is not so because it is dogmatic and requires faith.