On my system, ttyv0 and console are competing for keystrokes on the ttyv0-screen. This can be seen when logging in under X, immediately issuing
% xconsole -file /dev/console
in an xterm, switching to ttyv0 by pressing Ctrl+Alt+F1, and then typing some text.
In most cases, the typed text will appear in the Xconsole-window, and even if this doesn't happen immediately, hammering the keys fast enough with a few <Ret>s interspersed will usually make at least some characters appear in the Xconsole-window.
This might have security implications when parts of login credentials are redirected.
As an aside, things written to /dev/console invariably appear on the ttyv0-screen on my system, but are never passed on to xconsole.