Similar to Ubuntu Microsoft has decided to add a bit of resistance on the edges of a multi-monitor display setup. This allows the system to popup a menu (like the charm bar) before allowing your cursor to move to the next screen.
Please backup before doing any of this!
Navigate to HKEY_CURRENT_USER\Control Panel\Desktop\
Change MouseMonitorEscapeSpeed to 1 to disable (0 to enable).
Change MouseCornerClipLength to 0 (default is 6).
It will then require a restart for the changes to take effect.