Now that openvswitch-brcompat is not officially supported with recent kernels (Ubuntu 12.10 with kernel 3.5), the alternative to configure the bridges directly in the interfaces file has change a bit… but is still pretty forward!
Simple case with 1 bridge and 1 attached interface:
iface br99 inet dhcp
iface eth0 inet manual
And to bring it up and down:
ifup --allow=ovs $list_of_bridges
ifdown --allow=ovs $list_of_bridges
More info at: openvswitch-switch.README.Debian