Well I'm an idiot - the fulltext index on page_text was missing from a default installation. It didn't break searches but probably slowed them down tremendously. Also set engine to MyISAM on page_text to avoid cryptic error messages from MySQL.

// UK lang variables

tinyMCE.addToLang('flash',{
title : 'Insert / edit Flash Movie',
desc : 'Insert / edit Flash Movie',
file : 'Flash-File (.swf)',
size : 'Size',
list : 'Flash files',
props : 'Flash properties',
general : 'General'
});