I distribute software online, and always wonder if there is a proper way to better define version numbers.
Let's assume A.B.C.D in the answers. When do you increase each of the components?
Do you use any other version number tricks such as D mod 2 == 1 means it is an in house release only?
Do you have beta releases with their own version numbers, or do you have beta releases per version number?
I'm starting to like the Year.Release[.Build] convention that some apps (e.g. Perforce) use. Basically it just says the year in which you release, and the sequence within that year. So 2008.1 would be the first version, and if you released another a months or three later, it would go to 2008.2.
The advantage of this scheme is there is no implied "magnitude" of release, where you get into arguments about whether a feature is major enough to warrant a major version increment or not.
An optional extra is to tag on the build number, but that tends to be for internal purposes only (e.g. added to the EXE/DLL so you can inspect the file and ensure the right build is there).