By now #friendica is using regexps in the sql queries for searching for entries:
$sql_extra .= sprintf(" AND 'item'.'parent' IN (SELECT distinct('parent') from item where ( 'author-link' regexp '%s' or 'tag' regexp '%s' or tag regexp '%s' )) ",
The problem is: It’s slow. AFAIK MyBB is using the built-in functions from MySQL to make full text searches like they are described here: http://dev.mysql.com/doc/refman/5.6/en/fulltext-search.html
Shouldn’t we switch to that mechanism as well?