Reasons for SVN:
# diffs (on the client means faster, offline and less strain on server)
# tagging/branching
# serving via apache2 makes all sorts of things possible (better karma management)
# SVN manipulates the filetypes and does not require any special instructions.
# Directories, renames, etc. are all versioned.
# Ability to use SVK (star merges, and more)
# Ability to do external includes (e.g. pear stuff into pecl/pearweb)

Reasons against SVN:
# larger checkout size
# svn tools not available in all distros by default
# $ID:$ equivalent does not generate consequtive numbering per file
# developers will need to learn to do some things differently
# is svn as flexible with encoding as CVS?
# svn doesn't have real tags