Picture a user with that one-button mouse that comes with the iMacs – it is really easy to accidentally click that thing even if your hand is just resting in the center of the mouse. Combine that with dialogs where accidental clicks are instantly applied and you have no idea what you accidentally clicked on it makes for a very frustrating user experience. “Oh no, I bumped the damn mouse again and now I’ve turned something off and I want to get it back but I don’t know what it was!!!”. Using Windows conventions of OK/Cancel/Apply you can just click the Cancel button and not worry about what happened because your existing settings will be preserved.

Ideally you would want a combination of the both so that you had some safety mechanism combined with the speed of a real-time preview. The Apply button could be dropped so that all changes were visible in real time (if they even had a visible impact on the application behind the dialog – it really depends on the application), but if the Cancel button was pressed things would still go back to the way they were before the dialog was opened.

BTW, modal dialogs don’t need to appear in the Windows taskbar when they cannot be hidden behind the applications main window ;)

I somewhat disagree with Tog’s take on the save as dialog. While I see his point, and wouldn’t mind a free floating “save as”, I’ve personally never had a problem with the current save as dialog because it’s re-sizable (it’s only “hulking” if you make it that way). Here is an example http://robrohan.com/wp-content/uploads/2007/01/MacSaveAs.mov (not to mention when I go to save a document I often know why I am doing it)

Most of the time in Mac the real modal dialogs – the “you can’t do anything until you deal with this” – are attached to the window they belong to (like the save). This makes sense to me because it links the need to deal with it with the window that requires action – whereas a utility or a configuration window might be opened for a longer amount of time while doing other things with the application.

I also see your point with “windows can get “lost” to Windows users not familiar with navigating multiple ones”, but I think the newer generation of computer clients – the ones who grew up with computers (e.g. ~45 year olds down (maybe 35 down)) can handle many windows quite easily – I know my 9 year old nephew can – and I know anyone can learn – my wife’s retired mom and dad can.

This is a touchy subject because it can easily degrade into a my OS is better than your OS discussion, but what I was trying to point out is that “common sense” to a windows only user is vastly different than “common sense” to a predominately Mac user which can lead to “but that doesn’t make any sense” conversations when working together.

Obviously, it’s up to you to decide which is better and more apropos for your own application.

While I don’t have a document supporting Microsoft’s user testing results, my guess is from my own personal experience is that the vast majority of Mac user’s are more adept at window management. As such, windows can get “lost” to Windows users not familiar with navigating multiple ones, and the taskbar doesn’t help when the modal dialogue doesn’t actually register as a button on the windows taskbar in the first place. Thus, it’s invisible to the user.

That’s effectively 2 problems, which Tog does recommend the fix for the second.