I have Dell XPS 15 i7 - 2360 with nvidia 525M (1GB) with optimus running Ubuntu 12.10 64 bit and have bumblebee installed for optimus. Recently I installed Gnome Shell to give it a try and found it sort of lagging under few scenarios though rest all is butter smooth. When I click on Date gnome 3 it appears as if a second has elapsed before the window is drawn. But others panel items like network or volume looks fine. In gnome 3 when I'm on dash with (window preview) if I remove any of the windows before the remaining windows reshuffle it takes about 2 seconds (noticeable clearly). Everything else is fine in both unity and Gnome Shell. What is causing this slowness? Is Gnome Shell is really slower?