codeblue - 11:23 pm on Sep 15, 2011 (gmt 0)
Hmm... After some testing I receive the "block this site" text without being logged in. Also did a test to see how long a visitor must stay on a site without having the message displayed back in the serps. For my results anything under 3 min will display the message when returning to google. Also tryed navigating multiple pages on a site and still received the message in the serps if under 3 mins.
That strikes me as much longer than a "short" click and return.