When you want to distribute your own sources without any .svn directories is sufficient to create an export of the project with this command:
$ svn export svn://path_to_repository projectname
But often I've not access to the repository, so I remove any .svn directory by hand.
For a couple of directories is not a problem but today I've a big project with hundreds of directory, so I realized a little script to help me:
$ find . -type d -name .svn -exec rm -r '{}' \;