With the system maintenance work on this morning (migrating the WordPress MU database back form MySQL 5.x–>MySQL 4.x) , we could not solve the performance problem completely. Nevertheless, we could speed up the response times of our weblog service noticeably

The performance problem of our weblog service is still persistent.
With the scheduled system maintenance work on Monday, we hope to get the
service as fast as it was before the update to WordPress MU 2.6.5.