(Update 03/31/2013: Please see my newer post on this subject for more accurate information about the launcher's multimonitor behaviour.)

The leaked build of Windows Blue Build 9364 looks a helluva lot like Windows 8 unless you run it on multiple monitors. One major difference to Windows 8 is that apps and the launcher can now finally run on different monitors at the same time. Another difference is the fact that in this build, the launcher always seems to be pinned to monitor 1. So if you press Windows-Key-Page-Up or Windows-Key-Page-Down while on the launcher, nothing happens. On Windows 8, the launcher will cycle merrily through all connected monitors using these hotkey combinations.

When launching an app on Windows Blue Build 9364, it will initially start on the same monitor on which the launcher is running. But when pressing Windows-Key-Page-Up then, the app will switch to the next monitor, leaving a solid color background on monitor 1, which makes me wonder, why the launcher isn't visible on monitor 1 now instead of the dull solid background color. You have to press the Windows Key once to make the launcher visible again on monitor 1 while the app is still visible on the other monitor. Had you done this on Windows 8 instead of Windows Blue, the app would have been switched to the background and the launcher would have taken its place, all on the same monitor.

It remains to be seen if this observation will hold true until the final release of Windows Blue. If so, it will make things definitely a bit easier if your process needs to be notified about visibility changes of  apps or the launcher on different monitors. While there already is a notification scheme in Windows 8 that lets interested subscribers know about the visibility state of  apps on the computer's monitors and whether the launcher is currently visible or not, it is a royal PITA to find out on which monitor the launcher is currently located on Windows 8. Since there is no documented way of doing that, you have to go to great lengths (read: going to the realm of undocumented stuff) to achieve this. Having the launcher always pinned to monitor 1 is definitely a great relief in this respect. However, it is also questionable whether the launcher always pinned to monitor 1 is acceptable for the majority of users. Remember that for the traditional desktop in Windows 7 there is no such limitation w.r.t. to the location of the start menu as there will be to its successor on Windows Blue, the launcher.