Searching the site searches by title, description, AND tags, but there is no way to search only by tags - the site just uses Google to search, and Google searches the whole page. Google quite possibly ignores the tags because they're presented as a contextless pile of tags, which Google probably associates with spam and SEO rather than legitimate content.

The tag "system" was added way back when search engines still cares about content tags and doesn't mean anything anymore. It would be nice to fix it (or get rid of it) for PJ 3.5 :]