A few things:
1. svndumpfilter can take multiple args, e.g.
$ svndumpfilter include /x /y /z > mydump
to include /x, and /y, and /z. It can’t, however, do both include and exclude at once. In theory, you can run multiple dumps when you later load them, so you could (sort of; see below) accomplish the sameish thing with
$ svndumpfilter include /x > mydumpx
$ svndumpfilter include /y > mydumpy
$ svndumpfilter include /z > mydumpz
2. HOWEVER, if you have ever MOVED a file within the repository between (in the example above), /x and /y, you can’t rely upon doing it piecewise. That’s because the references within the loading process during the load of /y will no longer be valid as they point to /x/whatever.
3. It is commonly suggested that one edit “Node-path:” entries within the dump in order to fix up directory structure issues. NOTE that you MUST also change “Node-copyfrom-path:” in the same manner. Trickily, Node-copyfrom-path is only present in nodes that were (surprise!) copied from another node. This is of course tied to 2. above.
What is all this about, you ask? Well, it turns out that if you have a single respository with a lot of sprawling projects all under /trunk, you might need to break them out. (For example, if you intend to upload your repository dump to someone like a CVSDude or Beanstalk).
The error message that got me was something like:
svnadmin: File not found: revision 91, path ‘/trunk/x/whatever’