WordPress Mass Management Tools lets you update WordPress the easiest way possible via SVN:
Yes, users can often self-install via Fantastico or similar programs, but what guarantee do you have that they’ll upgrade as soon as new releases become available? Letting users run old versions of web software is a great way to get hacked. This kit lets you take control of users’ installations by checking them out via svn and upgrading them en masse.
Learn more: WordPress Mass Management Tools.