I would like to highlight some of the more important changes about sarge r2. They have been placed in the official announcement not as noticeable as I would have hoped.
Notable Changes

Sudo has been changed to not propagate all environment variables to
subsequent programs to avoid security risks.  This change might affect
software that uses sudo.  Please see /usr/share/doc/sudo/README.Debian
for more details.

Miscellaneous Bugfixes

This revision adds important corrections to the following packages.
Most of them don't affect the security of the system, but may affect
data integrity.

	affix-kernel           Fix build failures with sarge's kernel
	backuppc               Fix possible backup archive corruption and
			       possible data loss when changing the
                               configuration file
	cernlib                License problems, repackaged
	cyrus-imapd            Don't remove mail data on package purge
	cyrus21-imapd          Note cyrus-imapd data loss on package purge in
                               upgrade documentation
	evms                   Fix address stack corruption leading to possible
			       data loss when activating degraded RAID-5
	exim4                  Fix mail delivery problems to hosts with AAAA
                               DNS records and unbalanced DNS
	f-prot-installer       Adjusted to work with recent releases
	fai                    Fix setup of lo device, replaced hardcoded name
			       of debian distribution in fai-cd, add missing
                               packages when calling fai-mirror

	glibc                  Update timezone data, fix NPTL for x86_64 (amd64)
	leafnode               Fix security issue (CVE 2005-1911)
	libchipcard            Don't remove user account on package purge
	mutt                   Fix possible attachments data loss

	perl                   Fix problem with utf-8/taint interaction
	                       Fix possible malloc-to-death bug, #227621

	rssh                   Fix security issue (CVE-2005-3345)

	slune                  Adjust to security fix in py2play, #326976

	sodipodi               Fix segfaults on 64-bit architectures

	tar                    Fix inability to work with remote devices
                               on non-i386, #356657