SVN, or any other version control system for that matter, should always be used when developing code. It doesn’t matter if it’s for a single person project, or a huge project involving hundreds of different developers. Version control is essential.
I’ve always found version numbering interesting, and wondered how they are thought up by companies. With Mozilla jumping Firefox from 3 to 30+ in a very short space of time (about 3 years, Google getting Chrome from 1 to 41 faster than you can say “Is this the latest version”, and Microsoft going from IE4 to IE11 in around 20 years, it doesn’t lead to a simple answer. I did a bit of research, and found that there isn’t a hard and fast rule on how to do it. Jeff Atwood over at Coding Horror covers this better than I ever could in his post “What’s in a Version Number, Anyway?”
In a nutshell, people don’t care about version numbers.