Recent Subversion versions allow to specify the maximum depth to use when updating a given target. You can e.g. specify that you only want the files in a given directory, but not its sub-directories. Or you want a given directory to be empty, or removed from the working copy entirely.
Let's consider you've checked out an entire working copy, with the following structure:
If you're not interested anymore in subdir2.1 and its content, you can issue the following commands:
> cd root/dir2
> svn update --set-depth exclude subdir2.1
Now dir2 only has file2.1, and an 'svn update' command that does not specify a '--set-depth' option will not bring back subdir2.1 or any of its content.
If you're only interested in the files inside dir1, but not the subdir1.*, you could do:
> cd root
> svn update --set-depth files dir1
This tells SVN to only get the files in dir1, but not its sub-directories
Similarly, you can use '--set-depth empty' to get an empty directory (this can be useful to ask for one of its sub-directories), '--set-depth immediates' to get the immediate sub-directories, and use '--set-depth infinity' to restore the default and get everything in a given directory.
On the reverse, if you have to checkout a working copy but you know you only need some parts of it, you can use the '--depth' option (not '--set-depth', go figure...) of the checkout command. Then you create your paths in your working copy, step by step:
> svn checkout --depth empty [repository URL] root
> svn update --set-depth empty root/dir1
> svn update --set-depth infinity root/dir1/subdir1.2
> svn update --set-depth infinity root/dir3
Hope this helps!