I came across a fun little bug with Safari and other Web Browsers (FireFox and Chrome) on the Mac OS X desktop when you run with two monitors.
I was using a TV display as a second monitor and had my main laptop monitor arranged underneath. The critical factor was that the OS X menu bar was positioned on the Laptop monitor. i.e. It was between the primary and secondary monitor.
When the Menu Bar is between the main display and the secondary monitor you can’t move a Browser window up on to the second monitor. This is an interesting bug that seems to impact many but not all applications. Lotus Notes, SameTime and Microsoft Office Applications seem to ignore the menu bar while Skype sees it as a boundary.
If you move the Menu Bar to the other screen these bounded applications can now move freely about the double desktop.
It will be interesting to see how OS X Mavericks behaves since it appears to be introducing the double menu bar. That looks to be a very welcome feature to avoid the need to mouse or track long distances between desktops to access menu bar features.