By default on a dual-monitor system, you’re going to get the app launcher on the left-hand side of both monitors, with an ultimately annoying magnetic sticky effect when you drag the mouse between monitors. Now, I understand the reasoning, and whether this is good or bad depends on how you use dual monitors. It sucks for me, I’m turning off the second launcher. Rumor has it that you can change Edge Stop Velocity with CompizConfig Settings Manager if you re-installed it. Wrong. Another rumor has it that turning off Sticky edges under System settings / Displays is supposed to do it. Wrong again—though you do have to turn it off as part of the solution. The right answer is going into the X config program (in my case, NVIDIA X Server Settings) and fiddling with the “Make this the primary display for the X screen” checkbox, until you have just one launcher, and when you do (if the monitors are on the wrong site) make your life easier, and just switch monitor cables. Trust me. You will win back hours per week in dual monitor sticky mouse frustration.
Update: check out this post on Ask Ubuntu.