Steven Frank starts a user-interface discussion: .dmg Files Considered Harmful (via Daring Fireball).
I had some of the same misgivings about .dmg files, but there are also drawbacks to .sit and .tgz archives in that it's still not obvious to the untrained user how to install the programs after download. At least you can more reliably put instructions into a disk image window.
It's possible to make disk images user-friendly provided they satify three requirements:
- They should open a window automatically. After double-clicking (mounting) the image file, too many images show up in My Computer and the desktop, both of which may be hidden. So it looks like nothing happened. I just checked NetNewsWire, and it gets this right.
- They should have instructions in the main window on dragging the program to Applications. Again, NetNewsWire gets this right.
- They should show the Finder toolbar inside the window, so that the user can actually drag straight to the Applications icon. (Yes, this won't directly help the few users who may have manually removed this icon from their toolbars, but the majority of users will benefit.) NetNewsWire fails this test. So the user has to do some kind of dance in a different window, avoiding interfering with the image's window, either by opening up a separate Applications view or by finding a toolbar that does exist in an unrelated folder window. There are many opportunites for error here, including the Applications window obscuring the image or vice versa.
It would be interesting to see a new user try out a disk image. Without that, all I can do is speculate.