The best feature is that it is window/document orientated, not application orientated, so you can drag and drop between documents easily, which brings me onto:
Drag and Drop.
[1] Drag a file onto an application in the Dock, it opens. Hold down command-option to force an app to open any file.
[2] You can Drag an icon a the top of the window in a document based application.
[4] You can use expose to show the desktop, get a file of the desktop and then drag it onto a finder window. Wait a couple of seconds and it brings that window to the front.
Another one:
[1] Hold down the command key and click on the title bar in a document based application and it shows you the path to that file.
[2] Do the same trick in Safari and it shows you the path to that file on the web-server.
Also, if you select four items, then double click on them, it opens those four items.
This may sound like common sense, but it actually doesn't work in windows. Instead windows just decides to open the file you have jut licke on.
I think people say Expose because it is new - but we lived without it! Ask the question in a year and people will say spaces.
I'm not knocking expose by the way, it is a very fantastic innovative feature.
I explained how it works to a windows user and they said - I don't need that, I've got the taskbar. I couldn't have explained it very well.
