In wmf.10 (T305216), the wbsearchentities API doesn’t seem to find any search results anymore, except for exact entity ID matches. (For example, searching Q42 finds Q42, i.e. Douglas Adams, but should also find Q42395533, the item about Q42. Searching Douglas Adams produces no results.)
The main end user-visible impact was Wikidata autocomplete not finding any result (adding this to avoid duplicate reports, as we got some users noticing this).