Since Mac OS X Leopard I use Spaces a lot. In the System Preferences, Expose & Spaces you can configure Spaces. You can also configure Applications to use everytime the same Space. So for example my iCal always opens on Space 3, Tweetie always on Space 1 and so on. This is nothing new but it is pretty usefull to arrange your workspace like that.
I also use Adium a lot so, often I copy past something form Safari, Evernote, Mail or another program to the Adium Message Window. But with Spaces I always had to drag the Adium Message Window to the Space of the Application or the other way round. But there is a pretty cool setting in Spaces. You can set an Application be on “Every Space”. So I set Adium to “Every Space” and I don’t have to move the Adium Message Window or a Application.
I know this is nothing new, but I just didn’t know about this function.