Annoying Software: OS X Lion
Don't you just hate it when a application grabs the focus away from the application you're working on.
Unlike Windows, it seems that OS X Lion has nothing to prevent one application from grabbing focus away from another, meaning that while you're typing the ultra secret banking password into a website, another application, say Parallels or iTunes can request focus and without noticing it, you've typed your password (in clear text and for the world to see) in the newly focussed application.
OS X Lion can simply ignore any request from any application to receive focus unless it is the active application. Alternatively, OS X Lion can solve this problem by implementing a priority based queue for focus. Therefore if a user starts iTunes (which says takes 30 seconds to start), and immediately thereafter starts a browser such that it has focus, then any request coming from iTunes to have focus should be disregarded.
In addition, Apple can reject any application in the AppStore that attempts to take focus away from another application.
Windows does a pretty good job at it.