However, though the tutorial 1 by Till categorically states that it deals with "fail over, load balancing and high availability", but is it only me that I see no such things except syncing with unison /var/mail and /var/www?
Seems as if you did not read the full guide yet othwise you might have noticed that it contains also a synchronisation of the clinet databases trough mysql and it instructs you to install ispconfg as well in mirroe mode which does the configuration sync between the systems.
The complete setup required for this kind of failover is described in guide 1). All configuration mirroring etc. is done by ispconfig, all you have to do in case of a afilure is to switch the IP address like described by ovh or put a loadbalancer in front.