OS X uses them, GNOME 3 uses them, and for the Oneiric Ocelot so will Ubuntu.

What am I talking about? These: –

Also known as ‘Modal Dialogs’, ‘Modal Sheets’ and, in Ubuntu, ‘Slate Style Dialogs’, they� are best described as ‘a dialog box attached to one window and one window only’.

Better yet, they can’t be lost, don’t create entries in your taskbar/launcher and bear visual relation to the application they were borne from.

Image: Smspillaz