My apologies to users for the two hours of downtime tonight! While upgrading the server to PHP 5.4 (a new version of the software which powers MediaWiki), a configuration error caused the central script processor to be left at 5.3. This didn't work so well when the database access modules had been upgraded . . .
Page rendering should now be muchfaster (~15%). Memory usage has also decreased dramatically (~70Mb vs. 120Mb after a clean start).