Did you know that, when you are using an application - let's say Safari-, you could select some text (or some other things) from another application - let's say AdiumX -, without changing the focus?
Well, I don't know if that can be useful for you someday. I think it's interesting. And particularly it's interesting to know how many features of Mac OS X are "hidden" from casual users. They are there, but nothing tells you that it's there. If you discover by a way or another, it's good for you, and if you don't, well, you don't know what you miss and you don't really care...
Funny I forgot to tell you how! XD Simply press the Apple-key before you start clicking on the other application window! (and the focus won't change if you keep pressing the Apple-key when you are selecting from the other application window)