Svnsync has grown partial repository sync feature in 1.5

[Lieven Govaerts]

In the nightly build of the book (r2978), on the page about repository 
replication [1] there's a yellow box that says:

"The URLs provided to svnsync must point to the root directories of the 
target and source repositories, respectively. The tool does not handle 
mirroring of repository subtrees."

This has changed in 1.5. I've updated notes/svnsync.txt with a 
description of the actual situation. This is a copy-paste:

"
Q: Can I mirror a subdirectory of a master repository?

A: As of Subversion 1.5, it is possible to limit svnsync to a 
subdirectory of the master repository.
This is most useful when the master repository is organized in projects,
and you want to sync only one project.
Example showing svnsync of project1 in the master repository:
    /project1
       /branches
       /tags
       /trunk
    /project2
       /branches
       /tags
       /trunk

The following commands will sync all changes in /project1 to the target 
repository:
$ svnsync init file://`pwd`/dest 
http://svn.example.org/source/repos/project1
$ svnsync sync file://`pwd`/dest

Note: this syntax only allows you to limit the scope of svnsync to 
/project1. It does not:
- allow you to sync two or more projects from the master repository.
- recognize renames of project1. Example, if the original name of 
project1 was secretproject, only the changes starting from the revision 
in which the rename to project1 was committed will be synced.

If you need any of these abilities right now, you may want to look into 
SVK (http://svk.bestpractical.com/).
"

hth,

Lieven

[1] 
http://svnbook.red-bean.com/nightly/en/svn.reposadmin.maint.html#svn.reposadmin.maint.replication