OK... So I've got a stored proc that does some searching in the DB. Something like

DECLARE @ResultsOfFTSQuery TABLE (componentid int)
 IF (@FullTextSearch <> '')
 BEGIN
  INSERT @FTSResults SELECT ComponentID FROM Components WHERE CONTAINS (Rendering,@FullTextSearch)
 END

 SELECT TOP 10000 *
 FROM  TheTable WHERE
      (TheKeyID in (SELECT ComponentID FROM @FTSResults)) AND .....

And the performance gets REALLY bad as the results of the first query increases. Simply adding a PRIMARY KEY to the table variable increased performance from 40 secs down to sub 1 sec.

DECLARE @ResultsOfFTSQuery TABLE (componentid int PRIMARY KEY)

This article notes that you can't have 'real' indexes on table variables, but if you create a PRIMARY KEY or UNIQUE contstraint you get one for free.

I'm off to spend some time trying to find other procs I can optimise