I've always thought that one of the reasons SO was so successful is that they were an early adopter of easy to use markdown for code snippets, with a fairly snappy, simple UI.

Compare this with the alternatives around the same time, like Google Groups/Discussions or phpBB, which are still painful to look at to this day, IMHO. Is there anyone who wince when have to scroll through nested threads, and unformatted raw text in code to understand something?