how can I tell if a particular advisory/update has been installed?

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I am getting mail about updates that I should be applying to my system.  I did do the System->Administration->Software Update and got some updates.  Then when I did that again (immediately following the update), I had 328 updates that were all checked!  I'm pretty sure I don't want all of these, some appear to be architecture specific.  I read somewhere that there was something under Applications that could be used to "I think" view updates applied.  However, I don't have that.  I did find a file /var/yum/cache/.../rhel-x86_64-server-6/gen/updateinfo.xml.  Is this the updates I have?  Or the updates that are available?  When I get the advisory email notices from RH, I see something like RHSA-2012:1366.  I don't see anything like that in the list of System->Administration->Software Update to check against. 


And what are the icons to the left of each software update?  There's the green star thing, the yellow star thing with a bug, orange star with exclamation point...


Anyone want to recommend a good book to pick up on Administration?


What Patching Policy Should I Adopt For My RHEL Servers? discusses proactive versus reactive patching.


For most smaller environments, I would recommend adopting a proactive patching approach: make sure you have the right products and channels configured for your system, and then apply patches regularly (or even automatically). Red Hat puts a lot of effort in careful maintenance of RHEL, with various maintenance policies and lots of QA testing, all aimed at minimising the risks of errata introducing new issues.


Should you decide not to adopt a proactive patching approach, you can follow the steps from Is it possible to limit yum so that it lists or installs only security updates? to make sure don't miss out on security fixes.