In June 1-4, 2005 we had FISL 6.0 happening in Porto Alegre, RS, Brasil, which had more than 5000 participants (the count on the site is not accurate it seems).
We had a stand there, for CAcert and the Brazilian CAcert user group, in which we were doing assurances during the whole event.
We had assurance count way below our expectations, a little above 100, but we made very good contacts there, and many people got interested in the project but not confident enough to start using it yet. Many of those asked several times if there was really no cost, because commercial CAs are really unaffordable here, and the government-owned CA (ICP-Brasil) charges a good deal (R$ 400, about US$ 170) for a client certificate.
More pictures of FISL can be found here