Personally, I don't mind having to install another VCS to work on setup,
especially since the usage transition seems relatively painless, and if
only for the ability to do disconnected 'add's and 'diff's... It would
also give me an opportunity to play with subversion, learn it, and maybe
consider it for my local version control on other projects.
One thing, however, that did come up, and that I deem important, is that I
sometimes use the web interface to CVS (the CVSWeb that CGF mentioned) to
either track changes or retrieve an older version of some file. That and
the commit messages to cygwin-apps-cvs are pretty much essential for me,
so unless they could be done with subversion as well (and as nicely), I'd
have to speak out against the switch.
A wild idea: if there were some way to present a CVS view on a subversion
repository (i.e., have an adapter client that behaves exactly like cvs),
and to hook up that view to CVSWeb and anonymous read-only repositories
(so that people wouldn't have to use svn unless they mean to make changes
to setup), that would, IMO, satisfy pretty much everyone (including me).