Gnome shell installed through software centre does not display top toolbar panel properly (missing text and icons), and when one of the icons on it eg user's name is clicked the menu popup has missing text. Also when searching for application after pressing the super key, the filter list on the right is also missing random text letters often replaced by small rectangular  shape.
EDIT: It's the ATI drivers (using Mobility Radeon 5650), but after it's un-installed gnome-panel falls back to classic only and the system has to be reinstalled for the gnome-panel to work again. If the ATI drivers are not installed even the login screen lags when typing password. Also the ATI (post-release) driver never installs properly, the standard however does.