Hmm, how strange. I did a Repair from the Setup program and after rebooting it seems to be working OK now!
I did notice when I updated that there was a message - something about not being able to update some files as they were in use. If it's any help I did the update from the Update (Basic) settings page. When I updated my laptop earlier I used the 'Updating' option from the system tray icon and that didn't cause the problem...