I voted to remain visible. I assume that resource is not a problem for YC. This fact, coupled with YC not having a search feature, leads me to believe that it's better for YC community that this site is indexed by more than just one search engine. One big reason, as pointed out by Tichy, is that not all of us use Google as our primary search engine. By cutting off Yahoo, MSN, etc, but not Google, you would essentiall…
What's the slippery slope?
That's reason I voted for "Remain visible to Yahoo, MSN search." Had option two been "Be invisible to all search engines.", then I would've voted for that one. But then YC would need to offer its own search.