My organization recently had an event disrupted by protesters due to the sensitive nature of a main issue, and it looked really bad for us. Turns out, they found our event through a Google Alert, which led directly to the page. They registered a couple of fake names, planted themselves in the event, and the rest is history.
So, this is a major privacy issue. Currently, EventSpot allows you to keep events off the calendars. Would it be possible to offer the option for events to be private from search engines, as well? In my personal experience, this involves robots.txt modifications, and a meta tag - nothing complicated. But, EventSpot users can't access those features.