For instance, I normally need to view hidden files if I need to edit a text file. You can just drag the text file straight onto a text editor like TextEdit, and it will open the file directly.
[robg adds: This also works in Camino, but not in Safari or OmniWeb. Since an application is nothing more than a fancy folder, you can also drag and drop an application into either browser's window to reveal the files in that application's bundle. This technique was mentioned back in 2002 in this hint, but since the browser landscape has changed dramatically since then (and the ability to see hidden files wasn't previously mentioned), I felt it worth publishing.]

