same network, I would think that this idea was ok. From my experience, however, most multihomed customers have their second connection to a different network. Hopefully this will change but it is reality for now.
Not only is it reality, it is, from the customers point of view, a good idea. Greater diversity is better redundancy. For technical reasons - we've seen examples of providers bringing down their entire network, and for administrative/policy reasons (provider xxx decides to triple prices on their new contract). There is a solution to the customer who wants to be dual-homed to two providers and not contribute to the "routers can't handle the tables" problem. Just don't announce your more specifics to your backup provider unless you know your primary is down. Some type of automated script can do it.