I just recently started using Ubuntu (12.04) since a few weeks ago and noticed that the interface is very slow and sluggish:
On Dash, I have to type the entire app name and wait a few seconds before it shows up in the search box, and a bit later before it displays search result
Opening new files or applications takes also quite long and awkward
Dragging icons or moving app windows around is not very spontaneous too: I have to take extra attention in moving the mouse otherwise Ubuntu would not do a correct movement or might ends up doing something incorrect instead e.g. opening the windows to full screen options or move the file to different folders, which is frustrating
My PC is a few years old already (1.7 GB RAM) so this could be a reason too but when I checked in System Monitor it's hardly ever consuming much memory. Plus web-surfing on Firefox is actually lightning fast (much more than Windows), so I suspect there might be something wrong with the graphics driver (mine is GeForce 7050).
I checked around System Settings and found an option to update the Nvidia driver. So I tried it and restarted, as instructed.
Now, I got into a big problem upon restart... as the login-screen windows (where I have to type in the password) would take several attempts to display and finally did not manage to (it'd freeze for several seconds before there's any movement again). The background screen also kept reloading several times too and at some point the screen turned black with pixelated color strips running on the bottom 1/3 of the screen, and after a long while the background screen would come up again. Eventually I'd manage to be able to access the desktop but the launcher, top menu bar and app windows border would not disappear.
I searched around and found many other people have this similar problem after updating Nvidia driver too, and on some threads the suggestion is to use "killall -u $USER" in command line (it's the only thing among various online suggestions I could do, as at that point I could not access Terminal without the launcher - Ctrl-Alt-T doesn't work for me). So I did that and was able to access the desktop correctly again with launchee/menu by creating a new account. But I would still have the same problem if logging into my original account.
So I just finally tried upgrading to 12.10 and now can access my original account with fully-functional desktop - the launcher, menu and windows border are all back now.
However, the problem with sluggishness still remains. And now I get scared of ever having to update the Nvidia driver again!
I wonder if anyone knows what's the reason that updating the Nvidia driver is causing this problem and is there a way I can update it safely in the future? I'm still not sure how to solve the problem with the sluggishness too and not sure where else to look to find a solution.