ICM Registry, the company behind the .xxx top level domain, are getting into the search business.
This Thursday they’ll launch search.xxx, which is going to allow you to “search .XXX” ie. developed sites that use the .xxx top level domain.
If you use a .xxx domain name and want to find out about getting it indexed (or not) then they’ve prepared some information for webmasters here.
If for some reason you’d rather not have your site included in the search engine then ICM will respect your wish to “opt out”