While not strictly a protocol issue, one other concern has been raised by network operators who need to maintain autonomous systems with a large number of peers. Each speaker peering with an external router is responsible for propagating reachability and path information to all other transit and border routers within that AS. This is typically done by establishing internal BGP connections to all transit and border routers in the local AS.
In a large AS, this leads to an n^2 mesh of TCP connections and some method of configuring and maintaining those connections. BGP does not specify how this information is to be propagated, so alternatives, such as injecting BGP attribute information into the local IGP have been suggested. Also, there is effort underway to develop internal BGP "route reflectors" or a reliable multicast transport of IBGP information which would reduce configuration, memory and CPU requirements of conveying information to all other internal BGP peers.