I am not going to individually answer each question you've asked, as it seems there are already some pretty good answers. I would just like to explain the versioning scheme I use. Basically, I'm copying OpenBSD's scheme, except I don't release on a regular cycle. I think that's a good idea, but I don't make enough changes to justify that type of thing.

I start a project at 0.1, and for every release (e.g. every time I upload to CPAN, every time I make a .tar.gz for someone) I increment the minor number. If it's at .9, then I increment the major number. So 1.0 always follows 0.9.

I don't assign any special meaning to the major number; it's simply a function of how many releases I've made. I also don't have special stable/unstable branches. I can understand the reasoning behind these things, but I'm just not sure the extra complexity is worth it for the projects I work on.

Update: sorry for just updating the node, but my reply doesn't quite deserve a whole new node. gaal said:

You may as well use integers, no?

Yes, but I like X.Y version numbers. They make me feel warm and fuzzy.