Take a look at a pretty old email from Linus on cvs/svn vs git.. (2005).
So one of the worst downsides of CVS is _politics_. People, not technology.The upside of centralization is that a lot of things are easier. Easier to think about, easier to get a stupid and straightforward idea working. But if you have hundreds of developers, and you have a dynamic trust network (I trust some people, they trust others, and we all tend to trust people more or less depending on what they work on), the CVS model is absolutely HORRID. It just doesn't work.