Recently there was a bit of heated discussion on the development mailing lists (the good kind!) about module developers doing proper releases. The jist of it being that some modules never get a proper release tagged, and exist as a constantly changing ‘dev’ version that is mostly stable but at any time could contain showstopping bugs as new features are constantly added to the tree. Sure, you may argue that using a dev or release candidate on your site is bad practice, but often they are very stable (it completely depends on the maintainer) and necessary to use.