Since joining EvC, I have had to do a bit of research to write posts. I was amazed at how much evidence their is to support the theory of evolution. Before I joined, I thought that the main evidence was a plausibility argument along with a few fossils, and the Linnean classification.
I found out that not only was hierarchical classification much more detailed than I had thought, and that the fossil record was also much, much more complete than I had anticipated, but there is a huge amount of detailed evidence in other fields as well that I had never thought of (like retroviral insertions).
So, my participation on this board (as well as reading other peoples' posts -- I don't want to dis other people!) has really increased my understanding of the main topic.