We're in the process of rolling out a redundant switch configuration in the data centre. As a part of this, we're re-configuring all our servers with bonded NICs. I ran into a bit of a problem with our xen machine in that I couldn't add a bonded interface to a bridge, which is required for xen networking.
It turns out that a patch to the ifcfg-eth script fixes the issue by creating the bonded interface before creating the birdges.
The patch is here: