Evolution is not proven fact, nor will it ever be. In fact, it cannot be proved. This is not because of lack of evidence, as many would think, but because of the very nature of the scientific method.
In the scientific method, one begins with a question that cannot be explained by existing theories. Using what one knows, which may include other theories of more or less credibility, one attempts to explain the phenomenon or answer the question by creating a new hypothesis. Typically, this hypothesis is published in a scientific paper, though this is not a fundamental part of the scientific method. Once the hypothesis is made known to the scientific community, scientists begin examining and learning more about the hypothesis, because most often the creator of the hypothesis himself does not know everything about it. Then, they use the hypothesis to make a prediction about what exactly will happen in something pertaining to the area of the theory, whether it is physics, biology, cosmology, etc. If the prediction is incorrect, the hypothesis is revised. However, if it is correct, then scientists continue to use it to make predictions. If the hypthesis continually makes predictions that are shown to be correct and there is viable evidence that it accurately describes the Universe in which we live, then it is considered a theory. The theory continues to be tested by making predictions and evidence for the theory continues to mount. The more evidence a theory has, the more reliable it is considered. However, at this point, the idea can go no further. No idea, no matter how brilliant, can be more than a theory. Why??? Because there is always a chance of a counterexample - a piece of evidence that contradicts the theory or a prediction that is wrong. There is always a chance that it will be falsified. Thus, science can determine nothing for certain.
A perfect example of this is Einstein's Special Theory of Relativity. In my opinion and the opinion of many prominent physicists, such as Dr. Lee Smolin, Special Relativity is one of the most beautiful theories to ever be conceived by a human mind. Essentially, it is beauty in mathematical form! Thankfully, there is also a tremendous amount of evidence for it - ranging from predictions about time dilation to the effect of constant velocity on physical objects. In fact, it is one of the most well-supported theories in the history of science. However, despite the clear evidence for it, Special Relativity is not a fact, for the simple reason that there is a chance that it could be falsified in the future. Nevertheless, because of the extraordinary amount of evidence for it, most physicists consider it to be an incredibly reliable theory.
Thus, even something with the extensive experimental support that Special Relativity has is not a proven fact.
Furthermore, we cannot allow any idea in science, no matter how experimentally well-supported it is, to be considered a proven fact because that would hamper the advance of science. Science is all about questioning what we know about the Universe. Old theories must always be questioned and subjected to the newer methods of verification each new generation devises to ensure that no counterexample is missed. Without this eternal process of testing, science would not be able to advance.
History gives us a perfect example of what happens when we elevate a theory to the status of fact. Galen was a medical doctor during the time of the Roman Empire whose genius caused him to create radical new theories, which were far more accurate than previous ideas. Because of this accuracy, Galen became a renowned doctor and his theories began to be accepted by the physicians of that period. However, after his death, his theories became scientific dogma. Those who dared to question the words of Galen were deemed to be either ignorant or stupid. Evidence, clear and obvious, was dismissed because it disagreed with the theories of Galen. For hundreds of years, biology was at a standstill - unable to advance because it was choked by the dead hand of theories that were raised up to the level of facts. It was not until the rebellious Andreas Vesalius, who was truly a savior to science, published his work On the Fabric of the Human Body that the influence of Galen began to subside and his theories were allowed to be disproved.
Thus, if we allow theories to be hailed as proven fact; if we discourage and disallow the examination and citicism of established theories; if we mock those that attempt to do this, we hamper science. We do not allow it to properly advance and make progress. We choke it, almost literally.
There are currently a few very bright and intelligent young physicists in the scientific community who are questioning Special Relativity. They don't accept some of its basic assertions, such as the consistancy of the speed of light. They search for flaws within the theory and evidence that would disprove it. Are they to be mocked??? Are they to be considered ignorant or stupid??? Are they to be discouraged for doubting a well-established theory??? Of course not! They should be praised and commended for having the courage to defy Special Relativity. By doing so, they are ensuring that science continues to advance and make progress.
As a side note, I would like to point out that science can have multiple theories explaining the same phenomenon at once. For example, the dynamo theory and the rapid-decay theory are both theories of how the magnetic field generated by the earth came to be. Both string theory and loop quantum gravity are contenders for the theory of quantum gravity. Thus, you can have more than one valid theory to explain a phenomenon.
In conclusion, no theory can ever be proven and declared a fact. To do that would defy the scientific method and hamper the progress of science itself. Established theories must always be questioned in order that we might refine and replace them, as we attempt to discover the Theory of Everything that many scientists believe we will one day have.
Therefore, the Theory of Evolution cannot be and is not a fact, because there is always a chance it might be falsified. It must be continually questioned, like all theories, in order to eventually uncover the truth about our Universe.