yum update doesn't!

[Dave]

Newest problem ... since several have suggested updating my system would solve 
some issues, I tried it. "yum update" goes through, identifies all the 
packages that need updating (I assume--I didn't go through and manually 
verify), downloads all the packages (verified they're 
in /var/cache/yum/updates-released/packages), and then happily exits. But did 
it update anything? Nope. "yum check-updates" still lists everything that 
needed updating.

Am I supposed to manually go into the directory and run "rpm -Uvh *"? I 
thought yum was supposed to handle all that?