Just thought i would share this... i created it after
finding not finding anything with this functionality
(a while ago).  It was made for my personal needs 
initially, and was doctored up a few weeks later to
be somewhat customizable.  Its about a year old.

I have a cronjob that runs it every day:
0 1 * * * /home/conteb/cvs/snapshot.pl phynd /var/www/snapshots /var/cvs >> /var/www/snapshots/snapshots.log 2>&1

Sample can be found at http://www.phynd.net/snapshots/

#!/usr/bin/perl
#
# Create nightly cvs snapshots of project in a 
# repository, only saving the snapshot if the module 
# has changed.
# 
# TODO: Error checking is by no means complete.
#
use Date::Manip;

use strict;
use warnings;

sub printHelp; # print basic help screen

my $tempdir = '/tmp/';
my $maxdayspast = 90; # will only check 90 days in the past before recording.

# Can take 1 - 3 args - project name and dir to put resulting snapshot
my $project = shift(@ARGV) or printHelp;
my $dest = shift(@ARGV) or printHelp;
my $server = shift(@ARGV) or printHelp;


# test $tempdir, $dest for access and writabilty
die "Error: No access to /tmp or /tmp not a dir\n"
    unless (-w $tempdir && -d $tempdir);
die "Error: No access to $dest, $dest not a dir, or $dest doen't exist\n"
    unless (-d $dest && -w $dest);


# First checkout the needed cvs directory
chdir $tempdir;
if (defined $server) {
    (`cvs -d $server co -P $project 2>&1`=~/cannot find module/) and 
	die "Error: Invalid project specified - could not find module\n";
}

# get todays date and adjust acordingly...
my $date=$1 if &ParseDate('today')=~/(\d{8})/;

# create tarball
`tar czf $dest/$project-$date.tar.gz $project`;

# Now, find the last tarball
my $prev=1;
my $filename;
do {
    &DateCalc($date, "-".$prev." days")=~/(\d{8})/;
    $filename=$dest.'/'.$project."-".$1.".tar.gz";
    $prev++;
} while ((!(-e $filename))&&($prev < $maxdayspast));

# for some reason, compressed tarballs of identical trees checked out
# at different times create slightly different sized tarballs (on my 
# machine, anyway, using reiserfs).  I'm not about to step out of my 
# league and try to explain it - but it means we have to untar the package
# and run a diff on the two trees to see if there is a difference.
if ($prev == $maxdayspast) {
    print "Did not find any snapshots within $maxdayspast days, recording new..."; }
else {
    `mv $project $project.new`;
    `tar xzvf $filename `;
    if (`diff -Naur $project $project.new`) {
	print "Changes detected, recording snapshot...";
    }
    else {
	`rm $dest/$project-$date.tar.gz`; # dont save if nothing changed
    }
    `rm -r $project.new`;
}

# remove project directories
`rm -r $project`;
print "Done ($date)\n";
exit;

sub printHelp {
    print "Usage: snapshot.pl project destination_dir server\n";
    print "  project           name of project to check out of cvs\n";
    print "  destination_dir   where to put the snapshot\n";
    print "  server            server to connect to.  used as cvs -d server...\n";
    exit;
}