Turns out setting up ViewVC to do Subversion repository browsing was trivial once we had a mechanism to collect repository roots in one place.
For Subversion, I set up /var/lib/svnroots which has the same purpose as /var/lib/cvsroots. I set up a cron job to fill the svnroots directory with symlinks on a daily interval. All symlinks which points to repositories which don't have a "revision 1" are deleted, assuming that's a good indicator of which projects use Subversion.
The http://common-lisp.net/viewvc listing contains CVS and Subversion repositories sorted by alphabet.
Bye,
Erik.