yum update induces instability

[R. Hirschfeld]

I do "yum update" periodically to keep the system up-to-date, but the
recent report of instabilty introduced by an update gives me pause.
If "yum update" breaks the system in some way and it's not clear which
package is causing the problem, is there an easy way to recover the
previous state, reverting the updated packages to the previous update
(rather than the version on the CD)?  Is the information cached and
logged by yum sufficient to reconstruct the previous state?

Has anybody else experienced problems with the latest update or was
this an isolated incident?

Ray