I started with version 1.0 (no fuss about 0.X versions since GetBoo will probably never be really stable nor it will ever stop!).
Every subversions (dot something) are for minor changes, preferably not involving database changes (or at least nothing that is going to affect existing installations).
For major changes, including database changes where tables/rows are removed, another version number is preferred.

I will keep a changelog for each releases, writing the progress for each changes I make to the code (bugfixes included?).