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It is something switchers have a little trouble getting used to, but it has its merits. Some applications are nice to have always open without windows. Take browsers for example. They make you re-login to websites if you close them and reopen them. That's something that's really really bothersome about the Windows way of doing it. All of my friends leave their downloads window open in Firefox because of that fact. Other applications are better off closing when windows are closed, and some of them do! It'd also be nice if the OS could read your mind and know when you want an app closed and when you just want the window closed.
 
I think it would be more productive to talk about the apps we think should quit when last window is closed, rather than an all or nothing approach. It makes sense that iPhoto quits when you don't have an active window any more. The same would make sense for iTunes and Activity Monitor.

If I wanted Activity Monitor to be active in the background, I'd minimize it, if I wanted to quit, well I could quit, but why reach for the keyboard or mouse all the way up to the menu bar if I can hit the red button.
 
I think it would be more productive to talk about the apps we think should quit when last window is closed, rather than an all or nothing approach. It makes sense that iPhoto quits when you don't have an active window any more. The same would make sense for iTunes and Activity Monitor.

If I wanted Activity Monitor to be active in the background, I'd minimize it, if I wanted to quit, well I could quit, but why reach for the keyboard or mouse all the way up to the menu bar if I can hit the red button.

I always thought the same for Activity Monitor and was surprised when it didnt, but iTunes!?!? NO WAY. I close the window while it's playing all the time. Why do I need the window open?
 
What about flipping through Address Book photos like in Finder? THAT'S the one thing Apple should have done. ...unless I actually can?
 
What about flipping through Address Book photos like in Finder? THAT'S the one thing Apple should have done. ...unless I actually can?

Take a look at ~/Library/Application Support/AddressBook/Metadata using Cover Flow in Finder. You'll see the photos for each of your contacts (or the generic contact icon if the contact doesn't have one). Quick Look will show you the contact summary, and opening one of these files will launch Address Book to that contact record.

It's graceless, given the file names, but it technically makes what you asked possible. Perhaps at some point Apple will make this a built-in feature to further utilize Cover Flow, or someone could provide a plugin.
 
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