We were forced too to upgrade when we changed hosts.

The new one had a slightly older MySql 4 version so some tables (of our own support scripts) were not compatible at the new host. So we had to go for MySql 5. But ubb.threads 6.x was not MySQL 5 compatible.

In one day we upgraded everything on the old host, uploaded everything at the new place and beside a few DNS problems, we were up and running. All in all, about 9 hours of downtime.

[Linked Image from siemons.org]