I found a one-liner few days ago that exactly accomplished what I needed to do: add a lot of files with spaces in each filename that exist in various parts of a source tree to the subversion respository. I reproduce the line here, to ensure use for posterity:

svn status | grep "^?" | sed -e 's/? *//' | sed -e 's/ /\ /g' | xargs svn add

This one-liner is shamelessly ripped from Britt Selvitelle’s blog.