Facebook made its  profiles searchable and was bad about explaining those 34 million people on the site that Google will be able  to index FB users. This caused many visible bloggers to predict a dark future for Facebook (i.e., "It's over. I give FB six months.").  Also David Weinberger points out that

"FB could make this right with about two lines of code: Make exposing your FB info to search engines a matter of checking a box. What part of "opt in" does FB not understand?" 

As much as I am often in agreement with David, Facebook does exactly what he suggests already. In their privacy section they let users opt in (I highlighted the check box). It's a bit hidden (e.g., not on the front page highlighted in red) but it's clear and transparent. This will not be a repeat of the September 2006 "user riots."