a database update put the rathercurious site offline for many months.
I have not fully tracked down the fault (it occurs from a call in menu.php) and, frankly, have not had the time in recent months to given any attention to this site.
the problem manifested itself by a refusal of the admin site to load. Instead I got the message ‘You do not have permission to …’.
So I have finally taken the plunge and stubbed out the function causing the problem, exported the site data and reinstalled on a fresh WP 3.01 installation using mysql.
I have not given up at all on PDO for WP, nor on the sqlite driver. I am sure there will be a free week or so sometime during which I can have another look at it.