Comment 7 for bug 938448

I also ran into this bug tonight.

One workaround is the "Launcher Edge Stop Overcome Pressure" setting. You can set this number lower by installing CompizConfig setting manager . You can't set this to 0, unfortunately, but setting it to 1 did make a noticable difference to me. Directions for finding this setting can be found here: http://askubuntu.com/questions/109338/how-do-i-disable-mouse-magnet-on-middle-edge-with-multi-monitors

Another setting that looks promising is the setting called "Edge Stop Velocity".