Can you tell us how you submitted your site to Google? Was it the sitemap.xml file via Google Webmaster Tools?
At the moment search for guest is either ON or off. Is it possible to make max 10 search / usersession for guest or something?
Hm... other forum softwares throttle your search to one every x seconds, which we could do...
Though I really hated that "feature", to be honest
Yeah, but this is only for guest searches to minimize abuse!