Apple has released Mac OS X 10.6.8 and security update 2011-004.  These updates address 39 CVE entries.  The updates cover many components of the core operating system and many popular applications so you should probably plan to update ASAP.  The bulletin went out on Apple's security-announce mailing list, but the security update web page doesn't have the details yet, they should be there shortly.

Update 2011-06-24 16:30 UTC: As mentioned in the comments, some folks seem to have issues after applying the update and are subsequently unable to boot their machines.  Until we get some guidance from Apple and/or figure out exactly what is causing the issue, I guess we need to exercise a bit of caution updating critical machines (based on your own definition of critical).  There is a thread here discussing the issue, and another here suggesting the problem may be with PGP WDE, but I've heard from others who use PGP WDE who didn't have any issues, so I'm still not sure what the problem is.  Any of our users using PGP WDE who have successfully applied the update, please comment below or via the contact page.

References:

http://support.apple.com/kb/HT1222

http://support.apple.com/kb/HT4723 (info about the actual update)

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Jim Clausing, GIAC GSE #26
jclausing --at-- isc [dot] sans (dot) edu
SANS FOR558 Network Forensics coming to central OH in Sep see http://www.sans.org/mentor/details.php?nid=25749