bnt,
It could be the permissions. Just go Applications>Utilities>Disk Utility, click the top disk on the left hand side and then click "Repair Disk Permissions".
You can do the method described in your link to thexlab.com a little more easily by pasting the following into ScriptEditor, clicking "Compile", then "Run":
display dialog "The Finder must quit and will relaunch after the Launch Services rebuild is complete. The rebuild may take several minutes, during which time you should refrain from using any other apps." buttons {"Cancel", "Rebuild LS Database"} default button 2 with icon caution
ignoring application responses
tell application "Finder"
delay 2
quit
end tell
end ignoring
delay 5
tell application "System Events" to set running_applications_ to get name of every application process
if running_applications_ contains "Finder" then do shell script "killall Finder"
do shell script "/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user"
tell application "Finder"
delay 2
activate
end tell
tell me to activate
display dialog "The Launch Services rebuild is now complete." buttons {"OK"} default button 1 with icon note
Applemacster