Sometimes I need to get a few changes from the MythTV SVN server, that did not make it into the sources provided by JYA. To acomplish this I use the following command:

svn diff -r 23237:23242 http://svn.mythtv.org/svn/trunk/mythtv/ > 23237:23242.diff

Just change the two numbers at the beginning to those revision you want to have a patch for.