There have been a lot of complaints and criticism about Spaces in Leopard, particularly with how it switches spaces when you switch applications.
That behavior doesn’t really bother me, since a user action (clicking an application in the dock) initiates the space switch. When you click an application in the dock, that application should become visible. If it requires switching spaces to show that application, it’s only logical that it should switch to the appropriate space.
However, it should NEVER switch spaces on its own without any user action causing the switch. This is exactly what happens when an application in another space puts up an alert or displays a sheet. It also happens when you’re running Windows under either VMware or Parallels and some application (such as Outlook) displays a notification – in that case it’s especially annoying.
Instead of switching spaces, it could simply display some kind of notification in that application’s dock icon, either bouncing it or adding a badge (such as a yellow triangle with a ‘!’).
In fact as I was typing this blog entry (using MarsEdit in space 1), I received an email in Outlook, running in space 2, which switched me into that space, right in the middle of typing.