As a user, i've been occasionally fristrated with the decentralized nature of Maven. The isn't any single repository which would contain all packages (especially rc/beta versions). And in my experience repos and which repos are used to distributed a package tend to change fairly often. More often than not, I have to hunt for new repos when building from scratch.

Maven is also very slow when your project has ~10 repos and you need to download multiple dependencies. Having your own repo might be a necessity.