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 recently been approached about a project for me to work on, part-time and on the side. This itself isn’t unusual, but it’s one of a very small minority which I think is a good idea and has some promise. I’ll not go into details about it, as I don’t know the full details of what role I would be involved in, and to what extent, but I had a look into it over the weekend and discovered something which probably affects many small businesses initially, and something which could be disastrous for them. Their SEO sucks.