While trying to submit a patch to a drupal project, I ran into a problem creating a unified diff that could be suspected. It turns out that the way I was using the built in Subversion diff tool in NetBeans wasn't the way to go. Now, on the command line, I'm used to doing a "svn diff myfile.php > myfile.patch" to have a useable patch with the latest changes to a file. In NetBeans, I was thinking the same way, calling up a diff and then saving the output as a patch file – but that omitted crucial information like the name of the file to patch.
After hunting through the menus for a bit, I found the Export Diff Patch option in the Team menu. This is what you should use to create a unified patch that other developers can use. If you have the focus on a single file, it will generate a patch for just that file. If you click on a directory in your project and then create a patch it will include all changes for that folder.