Excellent small utility. It let you remove easily the dock icon of applications which should never have had an icon in the Dock (HardwareGrowler [in Growl:Extras], LaunchBar, ...) But it is easy to misuse it if you are careless:
WARNING 1. Dockless not only removes the dock icon, but also the menu bar. (Do read the ReadMe file!) Moreover, in some cases (when you log out...), the system could let a dockless (and menuless) application quit without warning you. Therefore, do not use Dockless with any app!
WARNING 2. Hiding dock icon and menu of an application does not affect you only, but every user (you cannot hide dock & menu for one user only).
WARNING 3. Dockless seems to not work properly with some apps (e.g., Preview.app, as noted in a previous review).