I really like the Perlish way of doing version numbering:

x.y.z, where x is the major release number, y is the minor release number, and z is the bugfix/patch count. (Recently, Perl started labelling development releases with an odd y, and production releases with an even y.) So for your example, fixing a minor output formatting bug might bring your program to 1.1.1, passing all of your tests consistently, and on all the platforms you want to support might bring it to 1.2, and adding substantial new features might bring it to 2.0.

Getting your version-control system to play nicely with this numbering system is left as an excercise.

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:wq