We use the same general naming convention that Eclipse uses. The version number consists of a three digit release number followed by a 12 or 15 digit qualifier. For example, a release carries the following version number: 6.3.0.r34x200912021814.
The first three digits change to reflect the major release or beta stream just as they do with Eclipse. As we put out major updates every 3-6 months, you will see those numbers change a couple of times a year. The qualifier portion of the version number, however, will change with every build so that they can be differentiated.