Spaces was one of the wild cards in Leopard that I wasn't too sure about going in. But now I can say, after using it for the past twenty-four hours, that it is one of the most useful and logical additions to Leopard. In fact, I might go so far as to say that Spaces is my new favorite app on Mac OS X.
As someone who typically needs to switch between windows constantly, Spaces was practically built for me. It gives you the option of creating up to sixteen "spaces", each with its own application assigned to it. Even better, you can bind an app to follow you regardless of which space you're in. In effect, this allows you to get back to that following app with a press of a button, making it the simplest way to get back to a critical app.
Although you can change the default, Spaces automatically maps to control+arrow key and control+number key, which is quite useful and needs no changing. You can also use an indicator button (I use F5) to activate Spaces. Upon hitting the button, the screen immediately changes to your Spaces configuration and allows you to quickly choose your option. That said, this is something that you probably won't use too often as long as you know which Spaces your programs are mapped to.
As an added note, Spaces even works with VMWare in Full Screen mode, so if you're a Vista user, you won't need to worry about Spaces becoming a headache that won't let you switch back and forth.
Without a doubt, the very best feature of Spaces is its ability to handle multiple windows of the same application. For example, let's say you have multiple browser windows in different spaces open and you start opening even more in each window. Upon clicking a link in a specific space, it will open in that space only -- none of the others. It may seem like a little thing, but consider the alternative: you would be switching back and forth between spaces just to find the appropriate window.
With up to sixteen spaces available, I found that after ten, it gets to be too much. That said, I can't imagine too many people will be using sixteen spaces. More often than not, I find myself using four to eight spaces and this is not only manageable, it's quite efficient in terms of space (pardon the pun) and usability.
All told, Spaces is outstanding. Prior to this, I had used Tiger and tried desperately to find ways to manage windows. But for the first time, I finally have a solution in Leopard that will do just that. I simply don't have any complaints with Spaces and once again, it only makes this operating system even better.
Overall Spaces grade: 10/10
Next up: Mail