Spaces is the desktop management scheme in Leopard, it allows you to have more than one space, before spaces most mac users used Virtual Desktop which had some benefits and some disadvantages over spaces. Spaces has the great ability to set a space for an app to open in so say you name your spaces like I do.

Space 1 = Communication Space 2 = Work Space 3 = Creative so when you start up you want to have mail and Twitterrific start in the communication space you can go in to system preferences and add the app to the list and then on the right choose the space and when you open iTunes you want it to go into the creative space you do the same, but set the space to space 3. In spaces you can choose how many space you have but your maximum is 16 but I can’t see any one using 16 spaces. One thing I miss is the ability to choose the animation between spaces but that is only minor. Spaces is a great addition to Leopard and one of the feature that will make you upgrade.