Forum Moderators: Robert Charlton & goodroi
robots.txt is useless for blocking googlebot in some instances, for example Google is ignoring robots.txt on pages with their +1 button, just something to keep in mind.
Googler, Jenny Murphy, provides a quick answer:
The +1 Button interacts with robots.txt and other crawler directives in an interesting way. Since +1's can only be applied to public pages, we may visit your page at the time the +1 Button is clicked to verify that it is indeed public. This check ignores crawler directives. This does not, however, impact the behavior of Google web search crawlers and how they interact with your robots.txt file.