If you want to know about NIC bonding combined with KVM usage, simply read the official KVM HOWTO. There are some known bugs with mode 0 and 6 (primarly used for load balancing), apparently the fix can be found on this page. For me to get the mode 1 (active-backup) working correctly i had to change the bonding config file as follows:

alias bond0 bonding
options bond0 miimon=100 mode=1 primary=eth0

and activate the STP protocol on the bridge. edit /etc/sysconfig/network-scripts/ifcfg-bridge0 and add

STP="on"