I find that most of the time, when I plug in my Dell 19" monitor with an HDMI lead, unity can't decide on the configuration; it will switch between different resolutions, and setups every 2-30 setusecond until I either ctrl-alt-backspace or unity crashes so I have to hard boot. Alternatively all the windows decorations and unity get killed. My setup is 11.10 64 bit,Dell Vostro 3550, AMD Radeon HD 6630M 1GB, Intel Core i5-2520M processor 2.50 GHz with integrated graphics card Currently I don't think the Radeon graphics card is working properly, but I'm not sure.