How come svn up subdir does not work when I check out a directory non-recursively (with -N) to reveal certain subdirectories?

Subversion 1.5 supports sparse directories. For Subversion 1.4.x, the workaround is to try checking out separate subdirectories of the repository and manually nesting your working copies.

Subversion 1.4.x, (see issue 695) the current implementation of svn checkout -N produces a working copy that has missing entries, and is ignorant of its "incompleteness". Subversion 1.5 addresses this issue by supporting sparse directories.

Since version 1.5