Some notes about my experience with the upgrade of a Trend Micro OfficeScan 10.6 to 11.0.
Check the version requirements before upgrading: Upgrade path to OfficeScan 11.0.
Basically, be sure to have the latest version of your current major version and service pack installed.
Check the system and OS requirements, as they have changed since 10.6 and 11.0. When upgrading, it is also recommended to create a backup, in case something goes wrong during the upgrade.
Upgrading from a version prior to 10, you may have to workaround losing your defined scan methods. This is not required when performing an in-place upgrade from any version 10 to 11.0.
It's always a good idea to create a backup of your server before the upgrade. In this particular case, the backup gets created right after disabling automatic upgrading of clients, as for the backup to be taken properly, you need to shut down the OfficeScan services. See the steps outlined below, and the articles mentioned therein, for more details.
Follow upgrade instructions: Upgrading OfficeScan (OSCE) server and clients.
In short, follow these steps.
After following the steps outlined, and consulting the articles I mentioned here, the upgrade went pretty smoothly. The important bit is not to skip steps and to carefully read the instructions in Trend Micro's knowledge base.