Sorry about last night's crash - it was caused by a problem regarding running SMF forums on an Ubuntu host.
What was happening was that due to the way Ubuntu handles php sessions by default, old sessions were not being deleted from the sessions tables and they just grew and grew from the time the server was upgraded a while back.
Across ukb/ukc there was something like a million records in the sessions tables - understandably this had a big impact on performance...but this should be fixed now.