I know that it's possible to get SVN to send emails after a commit using hooks, but I was just wondering if there's any way to create a personal "watch list" like MediaWiki (Wikipedia) has, whereby you only get notified if there have been changes to certain files?
One could certainly develop such a thing that would run as a Subversion hook. We had a similar system set up for CVS mailings at one place I worked at years ago.
Subversion itself doesn't have this capability built in, but I suspect there is at least one add-on out there that does this.
SVN-Monitor appears to have several monitoring options that can notify in many different ways. You can filter certain events to trigger certain types of notifications.
The way we take care of this is we have a watch property, you add your email address to that property in any directory and you get emailed about any changes in or below that directory.
The way this is achieved behind the scenes is that the post commit script checks every directory back to projects for each file in the commit reading the properties as it goes, from this it builds a list of email addresses to send the notification to. This takes a dozen or so lines of python.