It has been a Blender trademark that the user interface incorporated a non-overlapping window layout. Pre-2.5, it was impossible to move views so that they overlapped each other. This is no longer the case. Simply Shift+Click on the upper right of the view, and drag downwards and to the left. This will copy the view into an overlapping window, which can then be moved/scaled where ever you prefer.
Pros: You can have multiple overlapping windows if needed. This can be handy for running scripts in separate windows, or moving specific windows onto separate monitors.
Cons: Currently, there’s no way to keep a window on top while editing underneath. When you switch windows, the underlying window is forced to the top as the active window. You could use a hotkey to switch between the windows of an application (i.e. Mac OS X users can use Exposé to switch between the windows using F10, could be different depending on preferences).
Edit: I’m told there are some work-arounds for the overlapping windows to stay on top. They involve using the operating system’s window manager to do it. I don’t know of any way to do this in OS X, but I hear that linux users can do it. If someone knows, feel free to leave a comment about it.

