I can tell you that I do not do that. Typically if my BGP connectivity to a carrier fails I would prefer we don't route anything their way until we get that resolved because it might indicate a circuit that is up but unable to pass traffic (very common with carrier Ethernet especially). It does not guarantee anything but the BGP session is at least showing me that the last mile connectivity is good. In our MPLS VPN network we use BGP passwords that provide a bit of protection in case the carrier dumps one of our circuits into the wrong VRF (it does happen) and loss of the BGP session helps ensure that I don't route traffic into a MPLS VPN that is not ours.
Steven Naslund
Chicago IL