IIRC, SVK is an extension to subversion that provides a "personal repository", primarily to make it easier to do work in and update your own personal trunk while you and other people are working on big changes simultaniously. as far as I can make out, that's mostly useful when working on a project with many developers. Git and Monotone do something similar.

This kind of distributed approach might be useful to you, but if you are the only one working on the project and you can synchronize your repositories often enough (i.e. you plug in your laptop into your local network once a day) it's probably only going to add overhead.

If you are the only one/one of the few people working on projects, svn is probably good enough. The size of the project probably doesn't really matter. Also, svn is probably easier to get into your head than the distributed systems available. Personally, I use subversion. I might check out something more sophisticated if I was working with many people, but currently, I'm not, and for my own stuff svn is easy to work with, and it keeps all my code safe.