I've just found a fix to an annoying issue. I have a keystroke set to activate the screensaver and the lock the screen of my work MacBook Pro via an applescript. I was recently finding when I came back from lunch the system is pretty much dying on it's feet. I started poking around the system logs and googling some of the error message which all seemed to be related to coreservicesd.
From this post http://www.macosxhints.com/article.php?story=20071102105927735 I found the cause of the issue is that a second instance of the screensaver will kick in at the interval set-up in sys prefs despite the screensaver having already been manually activated when I lock the screen.
The solution for this is to activate the screensaver via an automator script as the link above describes. What I've done is to set the activation of the screensaver to never happen so that I always activate it manually.