I have been using Gnome 3.2 since Ubuntu 11.10 was released and it has always been perfectly smooth and performed extremely well, much better than Unity.
After doing a clean installation of Ubuntu 12.04, Gnome 3.4 performs less well. If just one window of a relatively simple application, such as Gnome Terminal, is opened and moved around, the movement is sometimes very choppy, but the rest of the time it's perfectly smooth. The times when it's choppy seem to be when part of the window goes off the bottom or right side of the screen. Also, if there are multiple windows open, it is almost always choppy. These facts suggest to me that it's something to do with the compositor.
Unity works perfectly smoothly. Memory usage is only at about 500-600MB, out of 3GB, even with a few things open. The graphics card is the on-board Intel graphics on the Core i5 M450.
Does anyone have any ideas what might be causing this problem?